WO2014072164A1

WO2014072164A1 - Pre-heating device for a fuel injection system

Info

Publication number: WO2014072164A1
Application number: PCT/EP2013/071951
Authority: WO
Inventors: Tadeu AMARAL; Roberta CRUZ; Fernando YOSHINO; Fabio Moreira; Juergen Stehlig; Patrik Klingbacher; Werner Schadler
Original assignee: Mahle International Gmbh
Priority date: 2012-11-09
Filing date: 2013-10-21
Publication date: 2014-05-15
Also published as: BR112015010105A2; DE102012220432A1

Abstract

The present invention relates to a pre-heating device (3) for pre-heating fuel of an internal combustion engine, comprising a housing (5) having an inlet port (6) for connecting the pre-heating device (3) to a distributor strip (2) of a fuel injection system (1) of the internal combustion engine and an outlet port (7) for connecting a fuel injector (4) of the fuel injection system (1) to the pre-heating device (3), a pre-heating chamber (10) that can be flown through by fuel and which is enclosed by the housing (5) and fluidically connected to the inlet port (6) and the outlet port (7), and further comprising at least one electrical heating element (12) for heating the fuel in the pre-heating chamber (10). In order to achieve a cost-effective structure, the respective heating element (12) comprises two opposing outer sides (13, 14), on which is arranged in each case at least one metallic heat transfer body (15, 16) which comes into contact with the fuel in the pre-heating chamber (10).

Description

Preheating device for a fuel injection system

The present invention relates to a preheating device for a fuel injection system of an internal combustion engine, which is arranged in particular in a motor vehicle. The invention also relates to a fuel injection system for an internal combustion engine, which is equipped with at least one such preheater.

In internal combustion engines, which are to be operated with a fuel which has a high viscosity at low temperatures, there is the problem that with the help of such fuels for the start of the internal combustion engine, ie for starting the internal combustion engine at these low temperatures no ignitable mixture in the Combustion chambers of the internal combustion engine can be generated. For so-called "biofuels", especially bio-diesel, this problem already occurs at temperatures below + 14 ° C. Other biofuels, such as, for example, ethanol and methanol, are characterized by a flashpoint of about 12 ° C., which is very high compared to the flash point of conventional gasoline, which is about -42 ° C. Consequently, such biofuels have a low volatility compared to gasoline and require a high heat of vaporization compared to gasoline Fuels, such as ethanol and methanol, to critical situations for starting an internal combustion engine under cold ambient conditions, since such biofuels require a large amount of heat to produce an injection jet suitable for ignition and engine starting.

This problem can be met with two fundamentally different approaches. In a first approach, for operating the internal combustion engine, a second fuel system can be provided, which it makes it possible to operate the internal combustion engine for its start with another, even at lower temperatures easily flammable fuel to start it. However, such a solution is very complex and therefore expensive. Furthermore, this results in the problem that the driver must monitor two different fuel tanks and their levels and this must not be confused when refueling.

A second approach is based on the general idea of preheating the poorly flammable fuel for the starting process of the internal combustion engine. Preheating the fuel increases its temperature and flammability. In particular, this reduces the viscosity. In this context, the preheating mentioned above are used.

From DE 101 40 071 A, a separate heating circuit for the heating of the fuel is known, wherein a specially designed for this injection nozzle has an additional connection for the heating circuit. Such a solution is complex and requires a comparatively large amount of space.

From DE 10 2009 001 062 A it is known to heat the fuel by heated valve air, whereby a special injection nozzle is also required here.

From FR 2 876 161 A it is known to integrate a heater into a fuel rail. In this case, a comparatively large volume of fuel is to be heated in order to be able to provide the preheated fuel for the starting operation. This requires comparatively much electrical energy and time. From EP 1 888 910 B1 a fuel injection system is known, which has a distributor strip for the provision of liquid fuel. Furthermore, a plurality of preheating devices of the type mentioned are provided, each containing a preheating space, each having a heating element and which are each connected via an inlet port to the distribution bar. Furthermore, a plurality of fuel injectors or injection nozzles are provided which are each connected via an outlet port to such a preheater. For each fuel injector, this results in a fuel path that leads from the distributor rail through the respective preheat space to the respective fuel injector. In the known fuel injection system or in the known preheating the respective heating element is designed as a glow rod or glow plug which protrudes coaxially into the respective preheating space. Furthermore, in the known preheating device, a housing containing the respective preheating space is made of metal and, when installed, welded to the distribution bar.

The present invention is concerned with the problem of providing for such a preheater or for a fuel injection system equipped therewith an improved embodiment, which is characterized in particular by a high performance and by a simple structure.

This problem is solved according to the invention by the subject matter of the independent claim. Advantageous embodiments are the subject of the dependent claims.

The invention is based on the general idea of equipping the respective electrical heating element with metallic heat transfer bodies, which come into contact with the fuel in the preheating space. Thus, the respective heating element heated primarily the heat transfer body, which in turn the Effect heat transfer to the fuel. As a result, the heating elements can be realized geometrically simple, for example, plate-shaped or as a flat cuboid. On the other hand, the heat transfer bodies can be purposefully realized so that they have a particularly large surface which can come into contact with the fuel in order to transfer the heat.

The invention proposes to use at least two heat transfer body per heating element, which are arranged on opposite outer sides of the heating element. The respective heating element is now used with the attached heat transfer bodies in the preheating so that the fuel is in contact with both heat transfer bodies. This results in a particularly intense heat transfer from the respective heating element via the heat transfer body to the fuel.

According to an advantageous embodiment, a first electrical connection and a second electrical connection can be provided on the housing, which can be connected to an electrical power supply in order to supply the respective heating element with electrical energy during operation of the preheating device. In the preferred embodiment, the first electrical connection is electrically connected to a first contact element, in particular directly, wherein the first contact element is electrically contacted with a first heat transfer body, in particular directly. The first heat transfer body is in turn electrically contacted with a first electrical connection of the respective heating element, preferably directly. The same applies to the second electrical connection, which is electrically connected to a second contact element, preferably directly, wherein the second contact element is electrically contacted with a second heat transfer body, preferably directly. The second heat transfer body is electrically contacted with a second electrical connection of the respective heating element, preferably directly. In this embodiment form the knowledge is exploited that the heat transfer body are metallic and are therefore electrically conductive. According to the above proposal, the heat transfer bodies are integrated in the respective electrical connection path, which leads from the respective electrical connection of the heating element to the respective electrical connection of the housing. This simplifies the electrical wiring within the preheater, since the heat transfer body can be used as components of the electrification of the heating elements. In the case of plate-shaped heating elements, in particular in the case of PTC elements, the two large outer sides facing away from one another form the two electrical connections of the respective heating element. By using the heat transfer body as an electrical conductor, the heat transfer body can contact a large area with the outer sides of the heating element. In particular, the heat transfer body can completely cover the respective outer side. Thus, the entire surface of the outer sides of the respective heating element can be used for heat transfer to the heat transfer body.

According to a particularly advantageous development, a first heating element and a second heating element can be provided. The first contact element electrically connected to the first electrical connection comprises a first contact section and a second contact section. The first contact portion of the first contact element is electrically contacted with the first heat transfer body of the first heating element, preferably directly, while the second contact portion of the first contact element is electrically contacted with the first heat transfer body of the second heating element, preferably directly. Also, the second contact element electrically connected to the second electrical connection has a first contact section and a second contact section. The first contact section of the second contact element is electrically connected to the second heat transfer element of the first heating element. clocked, preferably directly, while the second contact portion of the second contact element is electrically contacted with the second heat transfer body of the second heating element, preferably directly. By means of this structure, the two heating elements can be connected to the electrical connections in a particularly simple manner via their heat transfer bodies without complex line routing being required for this purpose.

In particular, the electrical contacts between the respective heating element and the respective heat transfer body and / or between the respective heat transfer body and the respective contact element can be realized such that the mutually contacting areas abut only loosely, so that, for example, solder joints and the like can be dispensed with , The electrical contact is thus made only by touch. Suitably, the contact elements may be configured as springs or their contact portions as spring elements, so that the respective contact takes place under mechanical bias.

In another advantageous embodiment, again a first heating element and a second heating element may be provided, the arrangement of the heating elements in the preheating space being such that a fuel path leading from the inlet port to the outlet port first fuels the heat transfer bodies of the one heating element and then the heat transfer bodies of the other heating element applied. The heating elements are thus arranged in series in the fuel path. By means of the series connection, a sufficient preheating of the fuel can be realized with a moderate supply of energy.

According to another advantageous embodiment, which can also represent an independent solution of the problem set in the beginning, is the Pre-heating chamber divided into at least two chambers, which are arranged in a leading from the inlet port to the outlet port fuel path, wherein in each sub-chamber at least one such heating element is arranged. In other words, the invention proposes to subdivide the preheat space into at least two chambers arranged in series in the fuel path. This makes it particularly easy to pre-heat the fuel in several stages, so that a sufficient preheating with moderate energy consumption is feasible.

According to another advantageous embodiment, the respective heat transfer body may have mutually parallel ribs which are spaced apart from one another transversely to their longitudinal direction and form between them flow channels, through which a fuel path guided from the inlet port to the outlet port is led. By means of such ribs, the surface of the heat transfer bodies available for heat transfer can be significantly increased, which correspondingly improves the heat input into the fuel. By selectively guiding the fuel path through the flow channels formed between adjacent fins, intensive contact of the fuel with the heated fins is enforced, which improves heat transfer to the fuel.

According to an advantageous development, the ribs may extend as far as a wall delimiting the preheating space, so that a substantial portion of the fuel path in the flow channels runs parallel to the ribs. In other words, the ribs are specifically adapted in terms of their dimensions to the preheating chamber, such that a fuel flow-through cross-section of the preheating chamber is substantially filled by the respective heating element and the heat transfer body attached thereto, so that as a free flow-through cross-section substantially only flow channels between the ribs are available. Thus, virtually the entire fuel flow is forced to flow through the flow channels. This results in a particularly intense heating of the fuel.

According to another advantageous refinement, the fuel path from the inlet connection to an end port facing the first heating element disposed in the first chamber, through the flow channels of the heat transfer body of the first heating element, from an end facing away from the outlet port of the first heating element to an end facing away from the outlet port second heating element, pass through the flow channels of the heat transfer body of the second heating element, from an outlet port facing the end of the second heating element to the outlet port. By this proposal, an intense heat transfer from the heat transfer bodies to the fuel as part of a series arrangement in the fuel path allows. Thus, a sufficient preheating can be realized in a compact space.

In another advantageous embodiment, the housing may have a housing opening through which the respective heating element can be inserted into the preheating space. The housing may now comprise a lid for closing the housing opening, which forms a carrier for the respective heating element and the heat transfer body. On this carrier, the respective heating element can be mounted with the heat transfer bodies outside of the housing, so that when attaching the lid to the housing, the respective heating element is used with the heat transfer bodies in the preheating. In other words, the lid is used here as an assembly aid by the components to be used in the housing, namely in particular the respective heating element, the heat transfer body and the optional contact elements are preassembled on the lid, creating a Pre-assembled module is created, which can be handled as a unit. When attaching the lid to the housing thus the components held there, ie in particular the respective heating element, the heat transfer body and optionally the contact elements are properly inserted into the preheating and kept in position.

According to an advantageous development of the cover can have electrical connections for supplying the respective heating element with electrical energy, wherein the respective mounted with its heat transfer bodies on the lid heating element is electrically connected independently of the other housing with these electrical connections. This means that the cover already carries the respective heating element fully functional, which in particular even outside the housing, a function check of the respective heating element or the entire preassembled module is possible.

According to another advantageous development, holding elements for fixing the at least one heating element and / or the heat transfer body may be integrally formed on the carrier, that is on the lid. The holding elements can basically be designed in the manner of locking elements or clip elements, which greatly simplifies the assembly of the respective heating element with the heat transfer bodies. In particular, can be dispensed with additional separate fastening means. The holding elements can work for example by means of positive locking. It is conceivable, for example, hook-shaped holding elements which are resiliently resilient and define plug-in areas into which the respective heating element with the heat transfer bodies can be inserted until the holding elements with their hook engage behind the heating element or the heat transfer body. Particularly advantageous is an embodiment in which the respective heating element is configured as a PTC element, in which the large outer sides facing away from each other form two electrical connections of the PTC element. In particular, in conjunction with the above-mentioned measures, a particularly inexpensive realizable embodiment can thus be provided for the preheating.

"PTC" stands for "Positive Temperature Coefficient." PTC elements are characterized by the fact that they convert electrical energy into heat, and at the same time their electrical resistance increases exponentially with increasing temperature. It is particularly simple to design elements in such a way that they can reach and maintain a predetermined temperature in a targeted manner at a predetermined temperature, without the need for expensive electronic regulation or control, since the electrical resistance of the PTC element becomes virtually infinite when the predetermined temperature is reached The use of such PTC elements thus makes it possible to achieve the desired preheating without the need for electronic control or regulation of the heating element, although in principle an electronic control can thus be omitted, but electronic control of reduced complexity can nevertheless be provided be to control and / or monitor the respective PTC element. For example, PTC elements can be realized particularly simply as flat plate bodies, that is to say as flat cuboids, with two outer sides facing away from each other and relatively large, which at the same time form the two electrical contacts or connections of the PTC element.

A fuel injection system according to the invention, with the aid of which combustion chambers of an internal combustion engine can be supplied with fuel, comprises at least one distributor rail for providing liquid fuel, a plurality Fuel injectors for introducing the fuel into the combustion chambers and a plurality of preheaters of the type described above. In particular, the preheating devices are connected directly to the respective distributor strip and the fuel injectors are each connected directly to one of the preheating. The fuel path then leads from the distributor strip through the respective preheater to the respective fuel injector.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

It show, each schematically:

1 is a greatly simplified isometric view of a fuel injection system in the region of a preheater,

2 shows a longitudinal section of the preheater, 3 is an exploded isometric view of the preheater;

Fig. 4 is an isometric view of the preheater

Fig. 5 is an isometric sectional view of the preheater.

According to FIG. 1, a fuel injection system 1, which serves to supply combustion chambers of the internal combustion engine with fuel in an internal combustion engine, not shown here, comprises at least one distributor strip 2, a plurality of preheaters 3 and a plurality of fuel injectors 4. The distributor strip 2, which is also referred to as a "rail" or " Common rail "can be used to provide liquid fuel. The respective preheater 3 serves to preheat the fuel before it reaches the respective fuel injector 4. For this purpose, the preheating devices 3 are fluidically between the distributor strip 2 and the respective fuel! Njektor 4 arranged. Accordingly, the preheating device 3 comprises a housing 5, which has an inlet connection 6, with which the preheater 3 can be connected directly to the distributor strip 2. Furthermore, the housing 5 has an outlet port 7, via which the respective fuel injector 4 can be connected directly to the respective preheater 3. For connecting the preheater 3 to the distribution strip 2, a first connector 8 may be provided. For connecting the injector 4 to the preheater 3, a second connector 9 may be provided. The respective plug-in connection 8, 9 can be designed as a "pure" plug-in connection, in which the components to be plugged into one another are plugged in. An additional fuse can then be provided to remove the plugged-in components Alternatively, the respective plug connection 8, 9 can also be used designed as a bayonet lock, in which a plug movement is combined with a rotary movement. Due to the rotational movement, a safeguard against pulling out can be realized.

According to FIGS. 2 to 5, the preheating device 3 comprises in its housing 5 a preheating space 10, which is fluidically connected to the inlet connection 6 and to the outlet connection 7. Visible in the embodiment shown here, the inlet port 6 is radially arranged with respect to a longitudinal central axis 1 1 of the housing 5, while the outlet port 7 is arranged axially with respect to the longitudinal axis 1 1. In preheating space 10, at least one electrical heating element 12 is arranged, which is preferably a PTC element which is configured as a flat plate body and has a rectangular cross-section. In this respect, the respective heating element 12 is geometrically a flat cuboid.

In the embodiment shown here, exactly two such heating elements 12 are arranged in the housing 5 or in the preheating space 10. These are expedient identical or identical.

The respective heating element 12 has two outer sides facing away from each other

13 or 14 on. The two outer sides 13, 14 thereby form electrical connections of the heating element 12, namely a first electrical connection, which is formed by the first outer side 13 and is also referred to below as 13, and a second electrical connection, which is formed by the second outer side 14 is and is also referred to below as 14. The mutually remote outer sides 13, 14 and electrical connections 13,

14 form the two largest surfaces of the respective flat cuboid.

Each heating element 12 is provided with two metallic heat transfer bodies, namely a first heat transfer body 15 and a second heat transfer body. Transmission body 16 equipped. The respective first heat transfer body 15 contacts the respective first outside 13 over a large area, while the respective second heat transfer body 16 contacts the respective second outside 14 over a large area. It is clear that in another embodiment at least on one of the outer sides 13, 14, more than one heat transfer body 15, 16 may be arranged so that ultimately the respective heating element 12 may then have three or more heat transfer body 15, 16.

The heating elements 12 are arranged with their heat transfer bodies 15, 16 in the preheating chamber 10 so that the respective heat transfer body 15, 16 is exposed in the preheating chamber 10 to the fuel and is in operation of the preheater 3 with this in contact.

The housing 5 has a first electrical connection 17 and a second electrical connection 18. The electrical connections 17, 18 serve to supply electrical energy to the heating elements 12. For this purpose, an electrical power supply can be connected to the electrical connections 17, 18. The first electrical connection 17 is directly electrically connected to a first contact element 19. The second electrical connection 18 is directly electrically connected to a second contact element 20. The first contact element 19 has a first contact section 21 and a second contact section 22. The second contact element 20 also has a first contact section 23 and a second contact section 24. The contact portions 21, 22, 23, 24 are in each case formed by a U-shaped bracket whose U-base carries two designed as spring elements U-arms. A connecting element 25 connects each of the two contact portions 21, 22 and 23, 24 electrically to one another at the respective contact element 19, 20. The contact elements 19, 20 are configured and arranged such that the first contact section 21 of the first contact element 19 is electrically contacted directly with the first heat transfer body 15 of the first heating element 12 shown on the left in FIGS. 2 and 3. On the other hand, the second contact section 22 of the first contact element 19 is in direct electrical contact with the first heat transfer body 15 of the second heating element 12 shown on the right in FIGS. 2 and 3. The first contact portion 23 of the second contact element 20 is directly electrically contacted with the second heat transfer body 16 of the left first heating element 12, while the second contact portion 24 of the second contact element 20 is electrically contacted directly with the second heat transfer body 16 of the right, second heating element 12. Furthermore, the first heat transfer body 15 is directly connected to the respective first electrical terminal 13 in the respective heating element 12, while the respective second heat transfer body 16 is contacted directly with the respective second electrical terminal 14 of the respective heating element 12. Thus, the electrical contact of the heating elements 12 with the electrical terminals 17, 18 on the one hand via the heat transfer body 15, 16 and the other via the contact elements 19, 20. For this purpose, the heat transfer body 15, 16 made of a suitable metal or of a suitable metal alloy , For example, it may be steel castings. Likewise, aluminum profiles or copper bodies are suitable. The contact elements 19, 20 are preferably made of spring steel.

As can be seen in particular from FIGS. 2 and 5, the preheating space 10 is subdivided into two chambers 26, 27 in the embodiment shown here. A fuel path 28, indicated by arrows in FIGS. 2 and 5, connects the inlet port 6 to the outlet port 7 and thereby passes through the preheating chamber 10 in such a way that it passes through the two chambers 26, 27 in succession. In particular, the fuel path 28 leads from the inlet port 6 to next through one or the first chamber 26 and then through the other or second chamber 27 to the outlet port 7. Preferably, in each of these two chambers 26, 27 each such heating element 12 is arranged with heat transfer bodies 15, 16. In that regard, results for the heating elements 12, a series arrangement or series connection with respect to their flow with the fuel along the fuel path 28th

As can be inferred in particular from FIG. 3, the heat transfer bodies 15, 16 each have a plurality of mutually parallel ribs 29 on a side facing away from the associated heating element 12, which are spaced apart from one another transversely to their longitudinal direction, so that they form flow channels 30 between them. These flow channels 30 also extend parallel to the ribs 29. Suitably, the fuel path 28 may be at least partially passed through these flow channels 30, so that ultimately a very large surface of the heat transfer body 15, 16 comes into contact with the fuel.

According to FIGS. 2 and 5, the chambers 26 and 27 and the heat transfer bodies 15, 16 or the ribs 29 can be matched to one another in terms of their dimensions such that the ribs 29 each extend as far as a preheating chamber 10 or the respective chamber 26 , 27 delimiting wall 31, 32, 33, 34 extend. In this case, the ribs 29, the respective wall 31, 32, 33, 34 touch or comply with this a relatively small distance. In any case, by this geometrical adaptation of the heat transfer body 15, 16 to the geometry of the chambers 26, 27 a substantial proportion, preferably more than 75%, in particular at least 90%, of the flow-through cross section of the fuel path 28 within the chambers 26, 27 the flow channels 30 passed. In this way, the fuel flow is forced in the operation of the preheater 3 to a large extent by the flow channels 30, so to flow between the ribs 29. In this way, the efficiency of heat transfer is significantly improved.

Here, the walls 31 and 34 are formed by mutually facing inner sides of a jacket 43 of the housing 5, which surrounds the preheating space 10. In contrast, the walls 32, 33 are formed by mutually remote outer sides of a partition wall 44 which extends in the preheating space 10 and thereby divided into the two chambers 26, 27. Thus, each face an inner side of the housing shell 43 and an outer side of the partition wall 44 and form the walls 31, 32 and 33 and 34, which limit the respective chamber 26, 27.

According to FIGS. 2 and 5, the fuel path 28 thus leads from the inlet port 6 to an end port 35 facing the outlet port 7 of the first heating element 12 arranged in the first chamber 26, through the flow channels 30 of the two heat transmission bodies 15, 16 of the first heating element 12, from an end face 36 of the first heating element 12 facing away from the outlet connection 7 to an end face 37 of the second heating element 12 facing away from the outlet connection 7, through the flow channels 30 of the two heat transfer bodies 15, 16 of the second heating element 12, from an end face 38 of the second facing the outlet connection 7 Heating element 12 to the outlet port 7th

As can be inferred in particular from FIG. 3, the housing 5 has a housing opening 39, through which the respective heating element 12 can be inserted together with the heat transfer bodies 15, 16 into the preheating space 10 or into the respective chamber 26, 27. The housing 5 now also includes a cover 40, by means of which the housing opening 39 can be closed. In the preferred embodiment shown here, this cover is 40th designed as a carrier for the two heating elements 12 and the associated heat transfer body 15, 16. For this purpose, the cover 40 has a plurality of holding elements 41 which protrude inwards from the cover 40, into the housing 5, in particular into the preheating space 10 or into the respective chamber 26, 27. The holding elements 41 may preferably be integrally formed on the lid 40, which is like the rest of the housing 5 is conveniently made of plastic. The holding elements 41 are designed here as latching hooks, which are elastically yielding transversely to their longitudinal direction and each have at their free ends a latching hook 42, with which the heating elements 12 and the heat transfer body 15, 16 can latch. This makes it possible, on the cover 40, the heating elements 12 with the heat transfer bodies 15, 16 outside of the housing 5 simple, namely in particular without additional separate fasteners to install, creating a pre-assembled assembly or unit is formed, which is uniformly mounted on the housing 5. Here, the heating elements 12 and the heat transfer body 15, 16 are introduced into the preheating chamber 10 and into the chambers 26, 27, while at the same time the lid 40 closes the housing opening 39.

On the lid 40, the electrical connections 17, 18 are provided. Likewise, then, the contact elements 19, 20 are in the preassembled state on the cover 40. The so preassembled module can be checked in particular outside the housing 5 on their electrical functionality, which in particular a troubleshooting is particularly easy.

Claims

claims

1 . Preheating device for preheating fuel of an internal combustion engine,

- with a housing (5) having an inlet port (6) for connecting the preheater (3) to a distributor strip (2) of a fuel injection system (1) of the internal combustion engine and an outlet port (7) for connecting a fuel injector (4) of the fuel injection system ( 1) to the preheater (3),

a fuel-flow preheating space (10) enclosed by the housing (5) and fluidly connected to the inlet port (6) and to the outlet port (7),

with at least one electric heating element (12) for heating the fuel in the preheating space (10),

characterized,

the respective heating element (12) has two outer sides (13, 14) facing away from one another, on each of which at least one metallic heat transfer body (15, 16) is arranged, which comes into contact with the fuel in the preheating space (10).

2. Preheating device according to claim 1,

characterized,

- That the housing (5) a first electrical connection (17) and a second electrical connection (18) are provided, which are connectable to an electrical power supply, - That the first electrical connection (17) is electrically connected to a first contact element (19) which is electrically contacted with a first heat transfer body (15) which is electrically contacted with a first electrical connection (13) of the respective heating element (12),

- That the second electrical connection (18) is electrically connected to a second contact element (20) which is electrically contacted with a second heat transfer body (16) which is electrically contacted with a second electrical connection (14) of the respective heating element (12).

3. Preheating device according to claim 2,

characterized,

that at least a first heating element (12) and a second heating element (12) are provided,

in that the first contact element (19) electrically connected to the first electrical connection (17) has a first contact section (21) and a second contact section (22),

- That the first contact portion (21) of the first contact element (19) with the first heat transfer body (15) of the first heating element (12) is electrically contacted,

- That the second contact portion (22) of the first contact element (19) is electrically contacted with the first heat transfer body (15) of the second heating element (12),

in that the second contact element (20) electrically connected to the second electrical connection (18) has a first contact section (23) and a second contact section (24),

- That the first contact portion (23) of the second contact element (20) with the second heat transfer body (16) of the first heating element (12) is electrically contacted, - That the second contact portion (24) of the second contact element (20) with the second heat transfer body (16) of the second heating element (12) is electrically contacted.

4. Preheating device according to one of claims 1 to 3,

characterized,

- That the heat transfer body (15, 16) of the first heating element (12) in a from the inlet port (6) to the outlet port (7) leading fuel path (28) upstream of the heat transfer body (15, 16) of the second heating element (12) are arranged ,

5. preheating device according to the preamble of claim 1, in particular according to one of claims 1 to 4,

characterized,

in that the preheating space (10) is subdivided into at least two chambers (26, 27) which are arranged one behind the other in a fuel path (28) leading from the inlet connection (6) to the outlet connection (7), wherein in each chamber (26, 27 ) at least one such heating element (12) is arranged.

6. Preheating device according to one of claims 1 to 5,

characterized,

in that the respective heat transfer body (15, 16) has mutually parallel ribs (29), which are spaced apart from each other transversely to their longitudinal direction and form flow channels (30) through which a fuel path guided from the inlet port (6) to the outlet port (7) (28) is passed.

7. preheating device according to claim 6,

characterized,

in that the ribs (29) extend as far as a wall (31, 32, 33, 34) bounding the preheating space (10), so that a substantial portion of the fuel path (28) in the flow channels (30) runs parallel to the ribs (29 ) runs.

8. Preheating device according to claim 5 and according to claim 6 or 7, characterized

in that the fuel path (28) from the inlet port (6) to an outlet port (7) facing end side (35) of the in the first chamber (26) arranged first heating element (12), through the flow channels (30) of the heat transfer body (15, 16 ) of the first heating element (12), from an end face (36) of the first heating element (12) facing away from the outlet connection (7) to an end face (37) of the second heating element (12) facing away from the outlet connection (7), through which flow channels (30 ) of the heat transfer body (15, 16) of the second heating element (12), from an outlet port (7) facing end face (38) of the second heating element (12) leads to the outlet port (7).

9. Preheating device according to one of claims 1 to 8,

characterized,

- That the housing (5) has a housing opening (39) through which the respective heating element (12) can be inserted into the preheating space (10),

- That the housing (5) has a cover (40) for closing the housing opening (39), for the respective heating element (12) and the heat transfer body (15, 16) forms a carrier, on which the respective heating element (12) the heat transfer bodies (15, 16) outside the housing (5) is attachable, so that when attaching the lid (40) on the housing (5) the respective heating element (12) with the heat transfer bodies (15, 16) is inserted into the preheating space (10).

10. preheating device according to claim 9,

characterized,

in that the cover (40) has electrical connections (17, 18) for supplying the respective heating element (12) with electrical energy, the respective heating element (12) mounted with its heat transfer bodies (15, 16) on the cover (40) independent of the remaining housing (5) is electrically connected to these electrical connections (17, 18).

1 1. Preheating device according to claim 9 or 10,

characterized,

in that holding elements (41) for fixing the at least one heating element (12) and / or the heat transfer body (15, 16) are formed integrally on the cover (40).

12. Preheating device according to one of claims 1 to 1 1,

characterized,

in that the respective heating element (12) is a PTC element whose mutually remote outer sides form two electrical connections (13, 14) of the PTC element.