KR20170050435A - Heater for electronic thermostat and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a heater for an electric thermostat and a method for manufacturing the same. The heater for the electric thermostat is heated depending on power supply; and controls opening and closing displacement. The heater for the electric thermostat is installed in a housing that forms a channel of coolant controlled by movement of a cylinder case, and defines an assembly space where the heater is assembled towards the inside from the outside. The heater for the electric thermostat comprises: a pair of lead wires; a heating element; a heating tube; a connector; a fixture; and a cover unit. The heating element is connected between the pair of lead wires. One end of the heating tube is closed. The other end of the heating tube is opened. An end part of the pair of the lead wires projects to the outside by inserting the heating element towards the closed one end from the opened other end. The heating tube is heated depending on heat of the heating element. The connector is connected to the pair of lead wires; and applies different polarity power. An upper part of the heating tube is inserted into a lower inner surface of the fixture. A lower outer surface of the fixture is inserted into a lower part of the assembly space. A lower inner surface of the cover unit is combined with an upper outer surface of the fixture. An upper inner surface of the cover unit surrounds a connection part of the pair of lead wires and the connector by enabling the outer surface of the cover unit to be inserted into the middle top of the assembly space.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater for an electronic thermostat,

The present invention relates to a heater for an electronic thermostat and, more particularly, to a heater for an electronic thermostat equipped with a heater capable of controlling the opening and closing displacement of a valve by heat generation according to the application of power, will be.

Generally, a thermostat for an automobile is installed between an engine and a radiator, and has a valve that is automatically opened and closed according to the temperature change of the cooling water, and controls the flow rate of the cooling water flowing into the radiator to maintain the cooling water at an appropriate temperature do. That is, the thermostat can control the temperature of the engine by controlling the flow rate of the cooling water according to the opening / closing displacement of the valve.

On the other hand, a thermostat for a vehicle is based on a mechanical thermostat having a structure in which expansion force of an expansion material such as wax expanding according to the temperature of a cooling water is transmitted to the piston to cause opening and closing displacement of the valve. A spring for supporting the valve, a capsule including an expansion material and a piston, etc. When the temperature of the cooling water is increased to a predetermined temperature (about 80 to 90 DEG C) The expansion material is changed from a solid state to a liquid state, and the expansion force generated by the volume change at this time is transmitted to the piston to operate the valve.

Since the mechanical thermostat thus constructed operates in accordance with the opening / closing temperature set at the predetermined temperature of the cooling water, that is, the valve is simply opened and closed at a predetermined temperature, There is a limitation in positively coping with changes in the driving environment or other conditions of the vehicle. In recent years, the electronic thermostat of the variable control system for maintaining the cooling water temperature of the engine at an optimum state while compensating for the disadvantages of the mechanical thermostat Stats are being presented.

Here, a general electronic thermostat is a structure including a connector for power supply and a cartridge heater for reacting an expansion material to the basic constituent elements of a conventional mechanical thermostat. In this case, a separate heat source The opening and closing timing of the valve is variably controlled by adjusting the amount of heat of the cartridge heater according to the traveling environment of the vehicle such as the speed of the vehicle, the temperature of the intake air, the load of the engine, and the like.

However, since the conventional electronic thermostat uses a two-step injection process such as a connector injection for fixing the heater to the connector and a connector for power supply, the size of the injection mold is increased As a result, productivity is reduced.

Korean Patent Publication No. 10-2014-0107341

An object of the present invention is to solve the above problems of the prior art by using a method in which only a connector is manufactured by an injection process and a connector and a heater are joined and connected to each other using an assembling mechanism, Thereby reducing the size of the mold and the number of process steps to simplify the manufacturing process and improve the coupling performance between the connector and the heater, and a manufacturing method thereof.

It is another object of the present invention to provide a heater for an electronic thermostat and a method of manufacturing the heater for a quick response by allowing the heat to be rapidly transferred to the expanding material by increasing the heat generating area.

In order to achieve the above object, a heater for an electronic thermostat according to the present invention is installed in a housing defining an assembly space in which a flow path of cooling water whose flow rate is controlled by the movement of a cylinder case is formed, A heater for an electronic thermostat, comprising: a pair of lead wires; A heating element connected between the pair of lead wires; A heat generating tube which is closed at one end and opened at the other end, the heat generating body being inserted from the other end to the other end so that the ends of the pair of lead wires protrude to the outside and heated according to the heat of the heat generating body; A connector which is connected to the pair of lead wires to apply power of different polarity; Wherein the upper end of the heat-generating tube is press-fitted into the lower inner surface and the lower outer surface is fitted into the lower end of the assembly space; And a cover portion which is engaged with the upper end outer surface of the fixing body and whose outer surface is fitted to the middle upper end of the assembly space and surrounds the connection portions of the pair of lead wires and the connector with an upper inner surface.

At this time, the bonding may be performed by a clamping method.

In addition, the upper end of the fixed body may be filled with an insulating material that maintains a space between the pair of lead wires.

In order to achieve the above object, the heater for an electronic thermostat of the present invention may further include an insulation tube disposed inside the upper end of the fixture to maintain a space between the pair of lead wires.

In order to achieve the above object, the heater for an electronic thermostat of the present invention may further include a sealing member fitted to the lower portion of the fixture.

In order to achieve the above object, the heater for an electronic thermostat according to the present invention further includes a thermally conductive element having an inner surface fitted to the outer surface of the lower end of the heat-generating tube and an outer surface having a larger surface area per unit length than the heat- can do.

According to another aspect of the present invention, there is provided a method of manufacturing a heater for an electronic thermostat, the method including: a connector for applying power; a heater for heating upon receiving power; The heater for an electronic thermostat includes a cylinder case. The heater for the electronic thermostat defines a flow passage for cooling water whose flow rate is controlled by the movement of the cylinder case, and defines an assembly space in which the heater is assembled from the outside to the inside. The method comprising the steps of: enclosing an upper end of the heater unit with a fixture having a lower end outer surface fitted into the assembly space; Connecting the power supply terminal of the connector and the power supply lead wire of the heater; And enclosing a connection portion of the heater portion and the connector with the upper end of the fixing body with a cover portion where the lower end inner surface is engaged with the upper outer surface of the fixing body.

Here, the bonding may be performed by a clamping method.

According to another aspect of the present invention, there is provided a method of manufacturing a heater for an electronic thermostat, the method including: fitting a sealing member to a lower portion of the fixture.

At this time, the step of enclosing the upper end of the heater unit with the fixing body may include: pressing the upper end of the heater unit in the lower end direction of the fixture body; And filling the upper end of the fixture with an insulating material that maintains the spacing between the pair of lead wires.

The step of surrounding the upper end of the heater with the fixing body may include the steps of covering the pair of lead wires with an insulating tube for maintaining the spacing between the pair of lead wires; And pressing the upper end of the heater part in the lower end direction of the fixture.

According to another aspect of the present invention, there is provided a method of manufacturing a heater for an electronic thermostat, the method comprising: forming a thermally conductive element having a large surface area per unit length on the outer surface of the lower end of the heater, Step < / RTI >

The present invention eliminates the injection process for joining the connector and the heater using a method of manufacturing only a connector by an injection process and connecting and assembling a connector and a heater, and by using a fixture, the mold size and the number of process steps So that the manufacturing process is simplified and the coupling performance between the connector and the heater is improved.

In addition, it has an effect of having a quick response performance by allowing the heat to be rapidly transferred to the expanding material by increasing the heat generating area.

1 is a cross-sectional view illustrating a heater for an electronic thermostat according to an embodiment of the present invention.
2 is a view for explaining a combination of a heater part and a connector of a heater for an electronic thermostat according to an embodiment of the present invention.
3 is a view for explaining a heating mechanism of a heater for an electronic thermostat according to an embodiment of the present invention.
4A and 4B are views illustrating a fixture among the heaters for an electronic thermostat according to an embodiment of the present invention.
5A to 5C are views illustrating a method of manufacturing a heater for an electronic thermostat according to an embodiment of the present invention.
6 is a flowchart illustrating a method of manufacturing a heater for an electronic thermostat according to an embodiment of the present invention.

The description of the disclosed technique is merely an example for structural or functional explanation and the scope of the disclosed technology should not be construed as being limited by the embodiments described in the text. That is, the embodiments are to be construed as being variously embodied and having various forms, so that the scope of the disclosed technology should be understood to include equivalents capable of realizing technical ideas.

Meanwhile, the meaning of the terms described in the present application should be understood as follows.

The terms " first ", " second ", and the like are used to distinguish one element from another and should not be limited by these terms. For example, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

It is to be understood that when an element is referred to as being "connected" to another element, it may be directly connected to the other element, but there may be other elements in between. On the other hand, when an element is referred to as being "directly connected" to another element, it should be understood that there are no other elements in between. On the other hand, other expressions that describe the relationship between components, such as "between" and "between" or "neighboring to" and "directly adjacent to" should be interpreted as well.

It is to be understood that the singular " include " or "have" are to be construed as including the stated feature, number, step, operation, It is to be understood that the combination is intended to specify that it is present and not to preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

Each step may take place differently from the stated order unless explicitly stated in a specific order in the context. That is, each step may occur in the same order as described, may be performed substantially concurrently, or may be performed in reverse order.

All terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed technology belongs, unless otherwise defined. Terms defined in commonly used dictionaries should be interpreted to be consistent with meaning in the context of the relevant art and can not be construed as having ideal or overly formal meaning unless expressly defined in the present application.

FIG. 1 is a cross-sectional view illustrating a heater for an electronic thermostat according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a heater part 300 and a connector 200 of a heater for an electronic thermostat according to an embodiment of the present invention. FIG. 3 is a view for explaining a heating mechanism of a heater for an electronic thermostat according to an embodiment of the present invention. FIGS. 4A and 4B are views for explaining a heating mechanism for an electronic thermostat according to an embodiment of the present invention. The electronic thermostat with a heater according to an embodiment of the present invention includes a housing 100, a connector 200, a heater unit 300, a cylinder case 400 And a guide 500. As shown in FIG.

The housing 100 forms a flow path of cooling water whose flow rate is controlled by the movement of the cylinder case 400, that is, the valve displacement, and the assembly of the connector 200 and the heater unit 300 is assembled The assembly space 110 can be defined. That is, the housing 100 corresponds to a pipe through which cooling water flows between a radiator (not shown) and an engine (not shown).

The connector 200 serves to connect the external power source and the lead wires 311 and 312 and has a pair of connection terminals corresponding to a pair of the lead wires 311 and 312, Current is applied. Here, the connection terminals of the connector 200 and the lead wires 311 and 312 may be joined together through clamping, laser welding, spot welding, or soldering, . ≪ / RTI >

The heater unit 300 is formed by combining the functions of the piston and the heat generating function in one structure and includes lead wires 311 and 312, a heat generating body 320, a heat generating tube 330, a heat generating mechanism 331, (340).

First, a pair of lead wires 311 and 312 are provided, one end of which is connected to an external power source through the connector 200, and the other end of which is connected to the heating element 320. That is, when the power is supplied through the connector 200, the lead wires 311 and 312 conduct current and transmit the conduction current to the heating element 320, so that the heating element 320 in the heating tube 330 Allow it to generate heat. For this, the lead wires 311 and 312 may protrude to the outside through one opened end of the heat generating tube 330.

The heating element 320 is connected to one lead wire 311 on one side of the lead wires 311 and 312 and one lead wire 312 on the other side of the upper side. At this time, when power is supplied to the lead wires 311 and 312, a current is transmitted to the heating element 320 through the lead wires 311 and 312 and the heating element 320 is heated as the current flows along the heating element 320 . Here, as the heating element 320, any material that generates heat as electric current such as metal or ceramic is used may be used, and its shape may have various shapes such as a coil shape, a cylindrical shape, and a plate shape.

On the other hand, the heat generating tube 330 has one end closed and the other end opened, and a heating element 320 is inserted from the other end toward the one end so that the ends of the pair of lead wires 311 and 312 protrude to the outside The one end portion of the heat-expanding material 410 is closed. Here, the heat generating tube 330 is inserted at one end closed to the inside of the thermal expansion material 410 such as wax, raises the temperature of the thermal expansion material 410 using the heat generated from the heat generating body 320, In addition, chemical corrosion by the thermal expansion material 410 of the heating element 320 can be prevented.

3, the outer surface of the heat generating mechanism 331 is connected to the outer surface of the lower end of the exothermic tube 330, and the outer surface of the exothermic tube 331 is made of a chromium wire having a large surface area per unit length, Is a thermally conductive element. That is, the heat generating mechanism 331 is a mechanism that compensates for the heat generating tube 330 having a cylindrical shape with a limited heat generating area, and can provide quick response performance due to rapid heat transfer through expansion of the heat generating area.

The insulating tube 340 prevents the current from flowing between the lead wires 311 and 312 and the heat generating tube 330 on the side portion where the pair of lead wires 311 and 312 are inserted in the heat generating tube 330 . At this time, a filling material (not shown) can be applied to the remaining space in the heat generating tube 330. Such a filling material is filled in the heat generating tube 130 into which the heat generating body 320 is inserted, And the heat generated by the heating element 320 is transmitted to the heating tube 330 while preventing the heating element 320 from flowing. Even if the power supply to the lead wires 311 and 312 is interrupted, foreign matter may be generated due to the ion change of the charged material due to the continuous power supply due to the ground current flowing in the vehicle. Therefore, As a filler. The insulating tube 340 may be connected to the fixing body 510 after covering the pair of lead wires 311 and 312 before the fixing body 510 is applied.

In order to maintain a space between the pair of lead wires 311 and 312 and between the lead wires 311 and 312 and the heat generating tube 330 after the application of the fixing member 510, A material (not shown) may be filled into the interior of the fixing body 510, and epoxy, Teflon, or the like may be used as the insulating material.

The cylinder case 400 accommodates the thermal expansion material 410 and moves back and forth along the heat generation tube 330 due to the volume change of the thermal expansion material 410. That is, the cylinder case 400 forms a valve for the cooling water flow path between the radiator and the engine, and controls the amount of cooling water supplied to the engine by converting the volume change of the thermal expansion material 410 to the displacement of the valve It plays a role.

At this time, the cylinder case 400 may have a structure in which the heat generating tube 330 is coupled to the heat generating tube 330 at an upper portion thereof so that the heat generating tube 330 can be inserted into the expansive material 330.

The thermal expansion material 410 is accommodated in the accommodating space of the cylinder case 400 and expands and contracts according to the heat generation and cooling of the exothermic tube 330, 400 to reciprocate.

The guide 500 surrounds the connection portion of the heater unit 300 and the connector 200 and is fitted into the assembly space 110. At this time, the guide 500 may include a fixing body 510, cover portions 521 and 522, and a sealing member 530.

The fixing member 510 surrounds the heat generating tube 330 and the lower end outer surface thereof can be fitted into the assembly space 110, that is, the lower portion can be press-fitted into the assembly space 110. [ 5A, an insulator tube 340 having a fixing guide formed on its upper portion is inserted into the exothermic tube 330 while surrounding the exothermic tube 330 with the fixture 510, And the exothermic tube 330 can be combined with each other.

The connector 200 and the heater unit 300 are connected to each other in order to eliminate the risk that the concentricity may be distorted as the connector 200 and the pair of lead wires 311 and 312 are connected to each other, And simultaneously fixes the heater 200 to the assembly space 110. [0052] As shown in FIG. Particularly, since it is difficult to make irregularities in the heat generating tube 330 of the heater unit 300, it is advantageous in terms of efficiency and economical efficiency of the manufacturing process to form various engaging irregularities on the fixing member 510.

4A and 4B, the fixing body 510 defines a space having a length 510a into which the heating tube 330 can be inserted, and the heating tube 330 can be easily press- A guide 512 may be formed and a jaw 511 may be formed to prevent the heat generating tube 330 from being pushed beyond a predetermined length 510a. In order to prevent the fixing body 510 from being cracked due to the pressing force of the heating tube 330 inserted into the fixing body 510, the outer diameter of the portion where the concave groove is formed on the outer surface of the fixing body 510 Since the thickness 510b between the inner diameters must be maintained at a predetermined thickness or more, the jaw 511, which is the end of the length 510a in which the heat generating tube 330 can be press-fit, does not overlap with the portion corresponding to the outer diameter of the recessed groove- As shown in FIG.

The cover portions 521 and 522 surround the connecting portions of the pair of lead outers 311 and 312 and the connector 200 of the heat generating tube 330 and the outer surface thereof is fitted to the assembly space 110 , And the lower end inner surface is engaged with the upper end outer surface of the fixing body 510. [ That is, the cover parts 521 and 522 are provided with a plurality of convex pieces and concave grooves, and the convex pieces and the concave grooves are engaged with the corresponding concave grooves and convex pieces of the connector 510 .

On the other hand, the sealing member 530 is fitted to the lower portion of the fixture 510. That is, the sealing member 530 is formed such that its inner diameter is fitted to the outer diameter of the exothermic tube 330, and the sealing member 530 is fixed to the lower portion of the fixing body 510 through the lower end of the exothermic tube 330 Respectively. Through this, the sealing member 530 can perform the sealing function when the apparatus of the present invention is applied on the cooling water flow path, so that the cooling water can be prevented from being introduced.

5A to 5C are views for explaining a method for manufacturing a heater for an electronic thermostat according to an embodiment of the present invention, and FIG. 6 is a flowchart showing a method for manufacturing a heater for an electronic thermostat according to an embodiment of the present invention. A method of manufacturing a heater for an electronic thermostat according to an embodiment of the present invention will be described with reference to FIGS. 1 to 6. FIG.

Here, Figs. 1 and 5A are sectional views cut in the same direction, and Fig. 5C is a sectional view taken in a direction perpendicular to Figs. 1 and 5A.

5A, the upper end of the heater unit 300, that is, the upper end of the heat generating tube 330 is press-fitted into the fixture 510, which is fitted into the assembly space of the housing 100, The portion 300 is press-fitted in the upper direction from the lower end direction of the fixing member 510 (S100).

The insulating tube 340 or the insulating shrink tube (not shown) having a fixing guide formed on the upper portion thereof before application of the fixing body 510, Is inserted into the exothermic tube 330 so as to surround the lead wires 311 and 312 to keep the gap between the lead wires 311 and 312 and the lead wires 311 and 312 and the exothermic tube 330 It is possible to prevent electricity from flowing.

When the heat generating tube 330 is not used, the heater unit 300 is press-fitted in the upper direction from the lower end direction of the fixing member 510 so as to press-fit the upper end of the heat generating tube 330, Can be filled with an insulating material that maintains a space between the lead wires 311 and 312 and between the lead wires 311 and 312 and the heat generating tube 330. Here, the filling material may be selected from materials having an insulating function such as epoxy or Teflon.

At this time, the heater unit 300 connects the upper side of the heating element 320 to one of the lead wires 311 and 312, and connects the other side of the upper side to the remaining one of the lead wires 312 And then inserting the lead wires 311 and 312 and the heating element 320 into the heating tube 330.

Thereafter, the connector 200 as shown in FIG. 5B and the lead wires 311 and 312 of the heater unit 300 as shown in FIG. 5A are connected and connected (S200). At this time, the connection terminals of the connector 200 and the lead wires 311 and 312 may be joined together by a method such as compression bonding, laser welding, spot welding or soldering, or may be combined by means of fitting or engaging.

Next, as shown in FIG. 5C, the cover part 521 and 522 surround the connection part between the upper end of the heating tube 330 and the heating tube 330 and the connector 200 (S300) The outer surfaces of the portions 521 and 522 are fitted into the assembly space 110 and the inner surface of the lower ends of the cover portions 521 and 522 are engaged with the upper surface of the fixing body 510.

Thereafter, the sealing member 530 may be pulled up from the lower portion of the heat generating tube 340 to the lower portion of the fixing body 510 (S400). At this time, the sealing member 530 serves to prevent the inflow of the cooling water in the case where the sealing member 530 is mounted on the housing 100 as shown in FIG.

On the other hand, the heat generating mechanism 331, which is a thermally conductive element, is fitted to the outer surface of the lower end of the heat generating tube 330 as shown in FIG. 3 (S500). At this time, since the outer surface of the heat generating mechanism 331 has a larger surface area per unit length than the heat generating tube 330, the heat generating tube 330 has a cylindrical shape to compensate the limited heat generating area, Fast response performance due to rapid heat transfer can be provided. Here, the heat generating mechanism 331 may be omitted, and this step may be omitted in the case of a structure in which the heat generating mechanism 331 is not provided.

5C can be assembled from the outside to the inside of the housing 100 in the assembly space 110 provided in the housing 100 forming the flow path of the cooling water.

According to the heater for an electronic thermostat and the method for manufacturing the same, as described above, overcoming the disadvantages of a shortened risk of short-circuit of the heater connection portion and reduction in durability caused by the manufacturing process of the double injection method of the conventional thermostat, It can prevent and improve problems that may arise in quality, and increase productivity by about 10%.

Although the disclosed method and apparatus have been described with reference to the embodiments shown in the drawings for illustrative purposes, those skilled in the art will appreciate that various modifications and equivalent embodiments are possible without departing from the scope of the present invention. I will understand that. Accordingly, the true scope of protection of the disclosed technology should be determined by the appended claims.

100: Housing
110: Assembly space
200: Connector
300: heater part
311, 312: lead wire
320: heating element
330: exothermic tube
331: Heating device
340: insulation tube
400: Cylinder case
410: Heat expansion material
510: Fixture
521, 522: cover
530: sealing member

Claims (12)

1. A heater for an electronic thermostat, the heater being provided in a housing defining an assembly space in which a flow path of cooling water whose flow rate is controlled by movement of a cylinder case is formed and from which the heater is assembled from the outside to the inside,
A pair of lead wires;
A heating element connected between the pair of lead wires; And
A heating tube which is closed at one end and opened at the other end and is mounted so that the heating element is inserted from one end to the other end so that the ends of the pair of lead wires protrude to the outside and are heated according to the heating of the heating element;
A connector which is connected to the pair of lead wires to apply power of different polarity;
Wherein the upper end of the heat-generating tube is press-fitted into the lower inner surface and the lower outer surface is fitted into the lower end of the assembly space; And
An electronic thermostat including a lower end inner surface which is engaged with an upper end outer surface of the fixture and an outer surface of which is fitted to the upper end of the assembly space and surrounds the connecting portion of the pair of lead wires and the connector with an upper end inner surface, Stator heater.
The method according to claim 1,
Wherein the bonding is performed by a clamping method.
The method according to claim 1,
Wherein the upper end of the fixed body is filled with an insulating material that keeps the spacing of the pair of lead wires.
The method according to claim 1,
And an insulating tube disposed inside the upper end of the fixture to maintain the spacing of the pair of lead wires.
The method according to claim 1,
And a sealing member fitted to the lower portion of the fixing body.
The method according to claim 1,
Wherein the inner surface is fitted to the outer surface of the lower end of the heat-generating tube, and the outer surface of the heat-radiating tube has a larger surface area per unit length than the heat-generating tube.
A heater for an electronic thermostat, comprising: a connector for applying power; a heater for generating heat upon receiving the power; and a cylinder case moving forward and backward on the heater in response to heat generated by the heater, A method of manufacturing a heater for an electronic thermostat, the method comprising: providing a housing for defining an assembly space in which a flow path of cooling water whose flow rate is controlled by movement of a case is formed and from which the heater is assembled from the outside to the inside,
Surrounding an upper end of the heater unit with a fixing member whose lower outer surface is fitted into the assembly space;
Connecting the power supply terminal of the connector and the power supply lead wire of the heater unit; And
And enclosing the upper end of the fixing body and the connecting portion of the heater portion and the connector with a cover portion whose lower inner surface is engaged with the upper outer surface of the fixing body.
The method of claim 7,
Wherein the bonding is performed by a clamping method.
The method of claim 7,
Further comprising the step of fitting the sealing member to the lower portion of the fixing body.
The method of claim 7,
The step of enclosing the upper end of the heater unit with the fixture may include:
Pressing the upper end of the heater part in the lower end direction of the fixture; And
And filling the upper end of the fixture with an insulating material that keeps the spacing between the pair of lead wires.
The method of claim 7,
The step of enclosing the upper end of the heater unit with the fixture may include:
Covering the pair of lead wires with an insulating tube for maintaining the spacing between the pair of lead wires; And
And pressing the upper end of the heater section in the lower end direction of the fixture body.
The method of claim 7,
Further comprising the step of fitting a thermally conductive element having a large surface area per unit length on the outer surface of the lower end of the heater to the outer surface of the lower end of the heater.

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