EP3234467A1

EP3234467A1 - Electric heating element and contacting system having improved durability

Info

Publication number: EP3234467A1
Application number: EP15816104.2A
Authority: EP
Inventors: Dietmar Hahn; Simon Schmittinger; Bruno CERON NICOLAT; Manuel Giesen
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2014-12-18
Filing date: 2015-12-08
Publication date: 2017-10-25
Also published as: WO2016096519A1; DE102014226433A1; CN107113922A

Abstract

The invention relates to an electric heating element (1), which contains an electrically insulating main body (11), in which a heating conductor (12) is embedded. At least two supply lines (13a, 13b) are led from the heating conductor to contact points (+, -), wherein said contact points can be connected to a current source arranged outside of the main body by means of contacting elements (14a, 14b), which are in flush contact. According to the invention, at least one first supply line (13a) is beveled at an angle between 5° and 80°, preferably between 30° and 50°, at the location of a first contact point (+), to which said at least one first supply line is led. It was discovered that a defined mechanical stop for the connection of the first contact point (13a) to the contacting element (14a) can thereby be created. It thus becomes possible to maintain the connection of the contact point (13a) to the contacting element (14a) by means of mechanical pressing. The success of the connection no longer depends on the durability of solder joints and welds. Likewise claimed assemblies of heating elements (1) according to the invention and specifically designed contacting elements (14a, 14b) are distinguished by significantly increased durability, in particular in the case of frequent temperature cycles, because of the improved connection between the heating conductor (12) and the contacting elements (14a, 14b).

Description

Description title

Electric heating element and contacting with improved durability

The invention relates to an electrical heating element and an arrangement of such a heating element and an associated contacting means.

State of the art

When starting a diesel engine, the hurdle must be overcome that the combustion chamber is still cold and the temperature for the auto-ignition of the fuel-air mixture is difficult to achieve. to

Startup support therefore glow plugs are used, which preheat the combustion chamber electrically. Such glow plugs are for example from the

EP 1 328 138 A1, from JP 4310565 B2, from EP 1 768 456 B1, from WO 2014/064279 AI and from WO 2010/071049 AI.

While the so-called preheating used to take several minutes, nowadays only a waiting period of a few seconds is necessary before the start. This is made possible by the fact that the ceramic glow plugs can be heated according to the cited references at rates of several hundred Kelvin per second and reach a temperature above 1000 ° C. after a few seconds.

The glow plug contains an electrical heating element that requires a supply line to the positive pole and a supply line to the negative pole of the vehicle battery for operation. The supply line for the negative terminal is usually provided by a corresponding on the outer circumference of the electric heating element

Contact point is provided. The heating element will go along this

Clamped in a holder on the glow plug, which in turn connected to the vehicle ground and therefore also to the negative pole of the battery. The connection with the positive pole of the battery is much more difficult. It has been found that a large part of the glow plug failures is not caused by a defect in the heating element itself, but by tearing off the connection to the positive pole of the battery.

Task and solution

It is therefore the object of the invention to provide an electrical heating element whose contact with the power source is more reliable than in the prior art.

This object is achieved by an electric heating element according to the main claim and by arrangements of such

Heating element and associated contacting means according to the independent claims. Further advantageous embodiments will be apparent from the dependent claims.

Disclosure of the invention

In the context of the invention, an electrical heating element has been developed, which contains an electrically insulating base body, in which a heating conductor is embedded. From the heat conductor at least two leads are to

Guided contact points, these contact points are connected by flush-contacting means with a arranged outside the main body power source.

According to the invention, at least one first lead at the location of a first contact point, to which it is guided, at an angle between 5 ° and 80 °, preferably between 30 ° and 50 °, bevelled.

It has been recognized that in this way a defined mechanical stop for the connection of the first contact point with the contacting means can be created. This makes it possible to maintain the connection of the contact point with the contacting means by mechanical pressing. In the prior art, this compound required a weld or solder joint made of a material that was less temperature-resistant than the heating conductor and the leads. At the high temperatures and extremely fast occurring during operation of the glow plug

Temperature fluctuations, these welds or solder joints have been found to be a weak point. By eliminating this shortcoming, the reliability of the connection is improved.

By being able to be held by pressing the connection between the contact point and the contacting means, it is self-centering and

self-healing. It should be due to different thermal

Expansion coefficients of body and contact means come to a relative movement between the contact point and the contacting, this movement is automatically after elimination of their cause back again. Solder joints and welds of the prior art could at best deteriorate under thermal stress and especially at repeated temperature cycles, but never improve again.

Furthermore, the resulting thermal stresses during heating of the heating element are partially deflected by the chamfered contact point, so that their tendency to interrupt the connection of the contact point with the contacting, is reduced.

The connection between the contact point and the contacting agent need not be held exclusively by pressing. It may, for example, additionally be secured by soldering or local melting of the contact zone. If these methods are used, pressing can be dispensed with altogether.

The contacting means may be connected in any way with a pole of the power source or an outgoing from it feed, for example by welding, soldering or local melting of the contact zone.

The supply line does not have to be chamfered along one plane. Your

Cut surface, along which it is chamfered, can also be curved. she may in particular run along a cone sheath. Such

Cut surface arises, for example, when a body with a embedded lead is cut conically.

For the main body, the heating conductor, the supply lines and the

Contacting agents are suitable at least for all those materials which have also been used according to the prior art. In particular, the base body may be a ceramic.

A heating element according to the invention does not necessarily have to be made from scratch. It is also possible to upgrade heating elements according to the prior art to heating elements according to the invention. For this purpose, for example, the heating element provided with a slope, there a

Contact point applied and these are connected to the existing supply line. Therefore, in a particularly advantageous embodiment of the invention, at least one of the contact points is connected to a supply line via an electrically conductive bridge running at least partially outside the main body. The bridge, for example, by a metal pin, a

Metallization on the surface of the body or be realized by a solder joint.

Advantageously, the base is cylindrical in at least part of the area between the two contact points. This cylinder is particularly preferably a circular cylinder. This shape is not only rotationally symmetric, but also the easiest to machine mechanically. However, the cylinder may also have a polygonal cross-section, for example.

In a particularly advantageous embodiment of the invention, the cylindrically shaped region of the main body opens into a cone or truncated cone. The first contact point is arranged in the region of the jacket of the cone or truncated cone, so that the heating conductor can be connected to the current source on a path leading through this jacket. In this case, the cone does not have a circular base, but can expressly have a polygonal base, so that its coat has edges. The designed as a cone or truncated cone portion of the body is on the one hand particularly easy to manufacture mechanically, such as by twisting. On the other hand, it enables a self-centering connection between the contact point and the contacting means in a particularly simple manner.

At least one second contact point is advantageously arranged in the region of the jacket of the region in which the base body is of cylindrical design. The heating conductor can be connected to the current source on a path leading through this jacket. Such a contact point is particularly easy to connect with a contacting agent. For example, it may be sufficient to clamp the cylindrical base body precisely in a cylindrical holder.

In a particularly advantageous embodiment of the invention, the heating element is designed as a starting aid for a vehicle engine. There are the requirements in terms of resistance to high temperatures and extreme

Temperature fluctuations particularly high. In such an environment, the more robust connection between the contact point and the

Contacting agent most likely to be noticeable.

A first advantageous arrangement of an electrical heating element according to the invention and an associated contacting means utilizes a cylinder, which is arranged on a cylinder of the vehicle engine and is connected to the vehicle mass, as contacting means. The connection to the contact point, which is arranged in the region of the cylinder jacket of the main body, is produced by inserting this cylindrical basic body into the cylindrical socket. Then, no additional line in the vehicle must be laid for the connection of the heating element to the negative terminal of the battery. Furthermore, the socket can be used to remove excess heat from the heating element. A particularly high temperature is needed only at the end of the glow plug, which is the combustion chamber in the cylinder

Vehicle engine faces. At the other end of the cylindrical

On the other hand, this body of heat on which the contacting means are arranged is undesirable. In a particularly advantageous embodiment of the invention, the

Arrangement a circumferential sleeve which is supported on the first contact point, as a contacting means. This sleeve can in particular run within a socket, in which the electric heating element can be inserted. The heat emitted by the heating element is not only emitted as desired in the environment of the heating element, but at the same time by heat conduction in both leads (plus and minus) coupled. A circumferential sleeve makes it possible to accommodate a large cross-section for the dissipation of this heat in a very small volume of construction. Furthermore, such a sleeve is particularly well suited for a self-centering mounting of the contact point of the contacting. The connection can be made, for example, by applying a biasing force between the heating element and the

Contacting agents are maintained.

Advantageously, the contacting means is designed as a spring element for exerting a normal force on the first contact point. In this way, a relative movement between the contacting and the contact point are allowed, while the electrical contact is also guaranteed at any time. Thus, in particular thermal expansions of the body can be collected without the electrical contact to the power source breaks off. For this purpose, the contacting means may be formed, for example, as a grid or mesh, which may then be stretchable in particular.

Advantageously, the contacting means for connection to the first

Contact point formed by means of an interference fit with the body plastically deformable. Such interference fit allows a particularly high contact pressure between the contact point and the

Contacting agent, which increases the stability of the compound.

Advantageously, the contacting means on a strain compensation area for receiving forces due to thermal expansion of the body. Then this thermal expansion does not necessarily mean that the contact force between the body and the contacting, and thus the quality of the connection between the contacting and the contact point, permanently weakened by frequent heating and cooling

Further measures improving the invention will be described in more detail below together with the description of the preferred embodiments of the invention with reference to figures.

In a further particularly advantageous embodiment of the invention, an at least partially bounded by the contacting means space is filled with a heat-insulating material. The room does not have to go through that

Contacting agent alone to be limited. To the boundary can

For example, the main body or a pole of the power source or an outgoing from such a pole lead to which the contacting is attached contribute. The thermal insulation reduces unwanted heat input, for example, to the pole, the lead or the connection of the pole or the lead with the contacting.

As a heat-insulating material are suitable in addition to air or vacuum, for example:

• a powder of metal, carbon or ceramic or other types of solid or hollow particles;

• a silicon resin or a cyanate resin;

A porous or cellular structure, such as a foam, made of carbon, ceramic or a metal

• or a combination of these materials.

Further, measures improving the invention will be described in more detail below together with the description of the preferred embodiments of the invention with reference to figures.

embodiments

It shows: 1 arrangement of an electrical heating element to a cylinder of a vehicle engine according to the prior art,

Figure 2 embodiment of the heating element according to the invention with

tapered body and circumferential sleeve as a contacting,

Figure 3 arrangement of tapered heating element and

Contacting agent with expansion compensation area,

Figure 4 arrangement of tapered heating element and spring element as a contacting and

FIG. 5 Conversion of a heating element according to the prior art to a heating element according to the invention.

Figure la shows the basic use of a heating element 1 for

Startup assistance on a cylinder 2 of a vehicle engine. The heating element 1 is guided through a hole in the wall 2a of the cylinder 2 into the combustion chamber 2e. Air can be sucked into the combustion chamber through an inlet valve 2b. Combustion gases can be expelled via an exhaust valve 2c. An injector 2d supplies the diesel fuel in the finest droplets.

If the piston 2f in the combustion chamber 2e moves upwards, the fuel-air mixture is compressed and heated so that it ignites itself. In the starting phase, when the wall 2a of the cylinder 2 is still cold, this is

Autoignition by preheating with the heating element 1, in a

Glow plug is enclosed, supported.

Figure lb illustrates the electrical contact and the internal structure of the heating element 1. The heating element consists of a base body 11 and includes a heating element 12, from the leads 13a and 13b go out. The supply line 13a is led to a first contact point +, which is connected by a solder connection with a contacting means 14a. The supply line 13b is connected by the lateral surface of the substantially cylindrical main body 11 with a second contact point. A metallic frame 14b, with the Vehicle mass is connected and into which the body is accurately inserted, serves as a contacting means for the contact point. Both

Contacting means 14a and 14b are connected to a current source 15.

Figure 2 shows an embodiment of the invention, in which a conically tapered body 11 via a peripheral sleeve than this

corresponding contacting means 14a with the positive pole 15a of

Power source 15 is connected. The main body 11 has an area IIa, in which it is formed as a rounding or as a truncated cone. When operating in a glow plug, this area is arranged in the combustion chamber 2e. A region IIb adjoins the region IIa along the longitudinal axis of the main body 11, in which region the basic body is circular-cylindrical. In this area, the contact point - is arranged, which belongs to the supply line 13b. By the base body 11 is inserted accurately in a connected to the vehicle ground socket 14b, the contact point - is connected to the negative pole of the power source 15 (vehicle battery).

The area 11c adjoins the area IIb, in which the base body is formed as a truncated cone. The supply line 13a opens into a contact point +, which lies on the lateral surface of the truncated cone 11c and is thereby bevelled. The circumferential sleeve 14a is supported on the mantle of the truncated cone 11c and thus also on the contact point +. It runs concentrically to the socket 14b. With the positive terminal 15a of the power source 15, the sleeve 14a is connected by soldering, welding, caulking or pressing. Around

To protect contact point from excessive heat by the heating element 1, the interior of the sleeve 14 a between the positive terminal 15 a and the truncated cone 11 c for the purpose of improving the thermal conductivity with a

Filling material filled 14al. The filling material 14al consists of a powder or a porous body, which is formed as metal, ceramic or as a mixture of metal and ceramic.

FIG. 3 shows the integration of a strain compensation region into the exemplary embodiment shown in FIG. The expansion-compensating portion 14a2 is disposed on the circumferential sleeve 14a between the truncated cone 11c and the positive pole 15a. If the elongated main body 11 thermally expands, the Expansion compensation area 14a2 on the resulting forces. If the main body 11 cools down again, the expansion compensation area 14a2 springs back, so that the prestressing force between the sleeve 14a and the contact point + is retained. The contact point is - as in the previous embodiment by the version IIb with the vehicle mass, and thus also with the negative pole of the

Power source, connected.

FIG. 4 shows the combination of a tapered heating element 1 with a contacting element 14a designed as a spring element 14a3. The spring element 14a3 has jaws 14a4, which against the spring force in

Press inside of the spring element 14a3. The plus pole 15a the

Current source 15 is pressed from the left against the jaws 14a4, so that even without soldering a connection with the contacting means 14a is given. However, this connection can be further strengthened, for example by soldering or welding. The heating element 1 with the tapered

Base 11 is pressed from the right against the jaws 14a4, so that the spring force exerts a normal force on the contact point + on the truncated cone shell at the end of the main body 11. The contact point - on the cylinder surface of the base body 11 is as in the previous embodiments by

Inserting the body in a metallic, connected to the vehicle mass socket 14 b contacted with this. The interior of the

Spring element 14a3 is filled with filling material 14al to prevent heat transfer to the positive pole 15a. 5 shows the conversion of a heating element 1 according to the prior art to a heating element 1 according to the invention. The left end of the main body 11 (area 11c) was as cylindrical as the adjacent area IIb before the conversion. The supply line 13a occurred in the region 11c in the

Central axis of the cylinder to the surface.

For conversion, the cylindrical shape was first ground to a truncated cone in area 11c. On the mantle of the truncated cone, a new contact point + was created by applying a metallization. This was made with a metallic bridge 16 with the from the central axis of the

Truncated truncated lead 13a connected. On the coat of the Truncated cone, and thus also on the new contact point +, the circumferential sleeve 14a is supported as a contacting. It is connected via a solder connection to the positive terminal 15a of the power source. The second contact point - which belongs to the supply line 13b - is connected to the vehicle ground via the holder 14b, in which the main body 11 is inserted. This closes the circuit.

Claims

claims

1. An electrical heating element (1), comprising an electrically insulating base body (11), in which a heating conductor (12) is embedded, and at least two supply lines (13a, 13b) from the heating conductor (12) to contact points (+, - ), wherein these contact points (+, -) can be connected by means of contact means (14a, 14b) lying flush with a current source (15, 15a) arranged outside the main body (11), characterized in that at least one first supply lead (13a) at the location of a first contact point (+), to which it is guided, at an angle between 5 ° and 80 °, preferably between 30 ° and 50 °, is chamfered.

2. Electric heating element (1) according to claim 1,

characterized in that at least one of the contact points (+) via an at least partially outside the base body (11) extending electrically conductive bridge (16) is connected to a supply line (13a).

3. Electric heating element (1) according to one of claims 1 to 2,

characterized in that the base body (11) at least in a part of the region between the two contact points (+, -) is cylindrical (IIb) is formed.

4. Electric heating element (1) according to claim 3,

characterized in that the cylindrically shaped portion (IIb) of the base body (11) opens into a cone or truncated cone (11c) and the first contact point (+) in the region of the shell of the cone or truncated cone (11c) is arranged so that the heating conductor (12) on a path leading through this jacket with the power source (15, 15 a) is connectable. Electric heating element (1) according to one of claims 3 to 4,

characterized in that at least one second contact point (-) is arranged in the region of the jacket of the cylindrical region (IIb), so that the heating conductor (12) can be connected to the current source (15, 15a) on a path leading through this jacket.

Electric heating element (1) according to one of claims 1 to 5,

characterized in that it is designed as a starting aid for a vehicle engine.

Arrangement, comprising an electrical heating element (1) according to claim 6 and at least one associated contacting means (14a, 14b), characterized in that the contacting means (14b) arranged on a cylinder (2) of the vehicle engine, cylindrical, connected to the vehicle ground socket is in which the electric

Heating element (1) can be inserted.

Arrangement comprising an electric heating element (1) according to one of claims 1 to 6 and at least one associated contacting means (14a),

characterized in that the contacting means (14a) is a circumferential sleeve which is supportable at the first contact point (+).

characterized in that the contacting means (14a) is designed as a spring element (14a3) for exerting a normal force on the first contact point (+).

characterized in that the contacting means (14a) for connection to the first contact point (+) by way of

Oversize fit with the base body (11) is formed plastically deformable.

11. Arrangement, comprising an electrical heating element (1) according to one of claims 1 to 6 and at least one associated contacting means (14a),

characterized in that the contacting means (14a) has a strain compensation region (14a2) for receiving forces by thermal expansion of the base body (11).

12. Arrangement according to one of claims 7 to 11, characterized in that an at least partially bounded by the contacting means space is filled with a thermally conductive material.