DE102012220432A1 - Preheating device for a fuel injection system - Google Patents

Abstract

The invention relates to a preheating device (3) for preheating fuel of an internal combustion engine, comprising a housing (5) which has an inlet connection (6) for connecting the preheating device (3) to a distributor rail (2) of a fuel injection system (1) of the internal combustion engine and has an outlet connection (7) for connecting a fuel injector (4) of the fuel injection system (1) to the preheating device (3), with a preheating chamber (10) through which the fuel can flow and which is enclosed by the housing (5) and which has the inlet connection (6 ) and fluidly connected to the outlet connection (7), and to at least one electrical heating element (12) for heating the fuel in the preheating chamber (10). An inexpensive construction is obtained if the respective heating element (12) has two outer sides (13, 14) facing away from each other, on each of which at least one metallic heat transfer body (15, 16) is arranged, which in the preheating chamber (10) with the fuel in Contact comes.

Description

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 "bio-fuels", especially bio-diesel, this problem already occurs at temperatures below + 14 ° C. Other biofuels, such as ethanol and methanol, are characterized by a flash point 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 low volatility compared to gasoline and require high heat of vaporization compared to gasoline. These properties result in critical situations for starting an internal combustion engine under cold environmental conditions in such biofuels, such as ethanol and methanol, since such biofuels require a large amount of heat to produce an injection jet suitable for ignition and combustion suitable for starting the internal combustion engine.

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 makes it possible to operate the internal combustion engine for starting 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 the DE 101 40 071 A a separate heating circuit for the heating of the fuel is known, wherein a specially designed injection nozzle has an additional connection for the heating circuit. Such a solution is complex and requires a comparatively large amount of space.

From the 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 the FR 2 876 161 A It is known to integrate a heater in 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 the EP 1 888 910 B1 For example, a fuel injection system is known that has a distributor rail for providing 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, the respective electric heating element with equip metallic heat transfer bodies, which come into contact with the fuel in Vorheizraum. Thus, the respective heating element primarily heats the heat transfer bodies, which in turn cause the 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, the knowledge is exploited that the heat transfer body are metallic and are accordingly 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 portion of the second contact element is electrically contacted with the second heat transfer body of the first heating element, 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, wherein the arrangement of the heating elements in the preheating space is such that a leading from the inlet port to the outlet port fuel path first the heat transfer body of the one heating element and then applied to the heat transfer body of the other heating element with fuel. The heating elements are thus arranged in series in the fuel path. Due to the series connection, a sufficient preheating of the fuel can be realized with moderate energy input.

According to another advantageous embodiment, which may also represent an independent solution of the problem set in the introduction, the preheating space is subdivided into at least two chambers, which are arranged behind one another in a fuel path leading from the inlet connection to the outlet connection, wherein at least one such heating element is arranged in each partial chamber , 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 can 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 cover is used here as an assembly aid, in that 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, whereby a preassembled assembly is formed, 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 lid is the respective one Heating element already fully functional carries, which in particular even outside the housing, a function check of the respective heating element or the entire pre-assembled 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", ie "positive temperature coefficient". PTC elements are characterized by the fact that they convert electrical energy into heat, while their electrical resistance increases exponentially with increasing temperature. Thus, PTC elements can be particularly easily interpreted so that they can reach a predetermined temperature targeted at a predetermined temperature and hold. In this case, no complex electronic control or control is required, since the electrical resistance of the PTC element when reaching the predetermined temperature is virtually infinite. The use of such PTC elements thus allows the desired preheating without the need for an electronic control or regulation of the heating element is required. Although in principle an electronic control can thus be omitted, nevertheless an electronic control of reduced complexity can be provided in order 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 strip for providing liquid fuel, a plurality of fuel injectors for introducing the fuel into the combustion chambers and a plurality of preheating devices of the type described above. In particular, the preheating devices are directly attached the respective distributor strip is connected and the fuel injectors are in each case connected directly to one of the preheating devices. The fuel path then leads from the distributor rail 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 a greatly simplified isometric view of a fuel injection system in the area of a preheater,

2 a longitudinal section of the preheater,

3 an isometric, exploded view of the preheater,

4 an isometric view of the preheater,

5 an isometric sectional view of the preheater.

Corresponding 1 includes a fuel injection system 1 which is used in an internal combustion engine, not shown here for supplying combustion chambers of the internal combustion engine with fuel, at least one distribution bar 2 , several pre-heating facilities 3 and several fuel injectors 4 , The distribution bar 2 , which can also be referred to as "rail" or "common rail", serves to provide liquid fuel. The respective preheater 3 serves to preheat the fuel before going to the respective fuel injector 4 arrives. For this purpose, the pre-heaters 3 fluidly between the distribution strip 2 and the respective fuel injector 4 arranged. Accordingly, the preheater includes 3 a housing 5 that has an inlet connection 6 having, with the preheater 3 directly to the distribution bar 2 is connectable. Furthermore, the housing has 5 an outlet port 7 on, over which the respective fuel injector 4 directly to the respective preheater 3 is connectable. To connect the preheater 3 to the distribution bar 2 can be a first plug connection 8th be provided. To connect the injector 4 to the preheater 3 can be a second connector 9 be provided. The respective connector 8th . 9 can be designed as a "pure" connector, in which the components to be plugged into each other only. Against an extraction of the inserted components can then be provided an additional backup. Alternatively, the respective connector 8th . 9 also be 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 the 2 to 5 includes the preheater 3 in her case 5 a preheat room 10 fluidly connected to the inlet port 6 and with the outlet port 7 connected is. It can be seen in the embodiment shown here, the inlet port 6 with respect to a longitudinal central axis 11 of the housing 5 arranged radially while the outlet port 7 with respect to the longitudinal axis 11 is arranged axially. In the preheat room 10 is at least one electric heating element 12 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 geometrically a flat cuboid.

In the embodiment shown here are exactly two such heating elements 12 in the case 5 or in the pre-heating room 10 arranged. These are expedient identical or identical.

The respective heating element 12 has two opposite outer sides 13 respectively. 14 on. The two outside 13 . 14 form electrical connections of the heating element 12 namely, a first electrical connection through the first outside 13 is formed and in the following also with 13 is referred to, and a second electrical connection, through the second outer side 14 is formed and in the following also with 14 referred to as. The outer sides facing away from each other 13 . 14 or electrical connections 13 . 14 form the two largest surfaces of the respective flat cuboid.

Every heating element 12 is with two metallic heat transfer bodies, namely a first heat transfer body 15 and a second heat transfer body 16 fitted. 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 the respective second outside 14 contacted over a large area. It is clear that in another embodiment, at least on one of the outer sides 13 . 14 also more than a heat transfer body 15 . 16 can be arranged so that ultimately the respective heating element 12 then three or more heat transfer bodies 15 . 16 can have.

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

The housing 5 has a first electrical connection 17 and a second electrical connection 18 on. The electrical connections 17 . 18 serve for the electrical power supply of the heating elements 12 , For this purpose is to the electrical connections 17 . 18 an electrical power supply can be connected. The first electrical connection 17 is with a first contact element 19 directly electrically connected. The second electrical connection 18 is with a second contact element 20 directly electrically connected. The first contact element 19 has a first contact section 21 and a second contact portion 22 on. Also the second contact element 20 has a first contact section 23 and a second contact portion 24 on. The contact sections 21 . 22 . 23 . 24 are each formed by a U-shaped bracket whose U-base carries two designed as spring elements U-arms. A connecting element 25 connects at the respective contact element 19 . 20 in each case the two contact sections 21 . 22 respectively. 23 . 24 electrically with each other.

The contact elements 19 . 20 are configured and arranged such that the first contact section 21 of the first contact element 19 directly with the first heat transfer body 15 in the 2 and 3 left illustrated first heating element 12 electrically contacted. The second Contact section 22 of the first contact element 19 is directly against the first heat transfer body 15 in the 2 and 3 right illustrated second heating element 12 electrically contacted. The first contact section 23 of the second contact element 20 is directly with the second heat transfer body 16 the left, first heating element 12 electrically contacted while the second contact portion 24 of the second contact element 20 directly with the second heat transfer body 16 the right, second heating element 12 electrically contacted. Furthermore, the first heat transfer body 15 at the respective heating element 12 directly with the respective first electrical connection 13 connected while the respective second heat transfer body 16 directly with the respective second electrical connection 14 of the respective heating element 12 is contacted. Thus, the electrical contact of the heating elements takes place 12 with the electrical connections 17 . 18 on the one hand on the heat transfer body 15 . 16 and on the other hand via the contact elements 19 . 20 , These are 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.

How in particular the 2 and 5 is the preheat room 10 in the embodiment shown here in two chambers 26 . 27 divided. One in the 2 and 5 indicated by arrows fuel path 28 connects the inlet port 6 with the outlet port 7 and is doing so through the preheat room 10 that he passed the two chambers 26 . 27 interspersed successively. In particular, the fuel path leads 28 from the inlet connection 6 first through the one or the first chamber 26 and then through the other or second chamber 27 to the outlet port 7 , Preferably, now in each of these two chambers 26 . 27 each such a heating element 12 with heat transfer bodies 15 . 16 arranged. In that regard, results for the heating elements 12 a series arrangement or series connection with regard to their inflow with the fuel along the fuel path 28 ,

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

According to the 2 and 5 can now the chambers 26 and 27 and the heat transfer bodies 15 . 16 or the ribs 29 in terms of their dimensions so matched to each other that the ribs 29 each to one of the preheat room 10 or the respective chamber 26 . 27 bounding wall 31 . 32 . 33 . 34 extend. The ribs can 29 the respective wall 31 . 32 . 33 . 34 touch or keep to this a relatively small distance. In any case, 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 inside the chambers 26 . 27 through the flow channels 30 passed. In this way, the fuel flow during operation of the preheater 3 forced to a large extent by the flow channels 30 between the ribs 29 pass therethrough. In this way, the efficiency of heat transfer is significantly improved.

Here are the walls 31 and 34 through facing inner sides of a shell 43 of the housing 5 Made the preheat room 10 encloses. In contrast, the walls are 32 . 33 by mutually remote outer sides of a partition 44 formed in the preheat room 10 extends and this in the two chambers 26 . 27 divided. Thus, each lie an inner side of the housing shell 43 and an outside of the partition 44 opposite and form the walls 31 . 32 respectively. 33 and 34 that the respective chamber 26 . 27 limit.

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

How, in particular 3 can be removed has the housing 5 a housing opening 39 , through which the respective heating element 12 together with the heat transfer bodies 15 . 16 in the preheat room 10 or in the respective chamber 26 . 27 can be used. The housing 5 now also includes a lid 40 , with the help of the housing opening 39 can be closed. In the preferred embodiment shown here, this lid is 40 as a carrier for the two heating elements 12 and the associated heat transfer body 15 . 16 designed. For this purpose, the lid 40 several holding elements 41 on top of that, from the lid 40 inside, in the case 5 into, especially in the preheat room 10 or in the respective chamber 26 . 27 into, stand out. The holding elements 41 may preferably be integral with the lid 40 be formed, as well as the rest of the housing 5 is suitably made of plastic. The holding elements 41 are designed here as latching hooks, which are resiliently resilient transversely to their longitudinal direction and at their free ends in each case a latching hook 42 have, with which the heating elements 12 and the heat transfer bodies 15 . 16 can lock. This makes it possible to the lid 40 the heating elements 12 with the heat transfer bodies 15 . 16 outside the case 5 simple, namely in particular without additional separate fasteners to install, creating a pre-assembled assembly or unit that is uniform on the housing 5 can be mounted. Here are the heating elements 12 and the heat transfer bodies 15 . 16 in the preheat room 10 or in the chambers 26 . 27 introduced while at the same time the lid 40 the housing opening 39 closes.

On the lid 40 are the electrical connections 17 . 18 intended. Likewise, then are also the contact elements 19 . 20 in preassembled condition on the lid 40 , The pre-assembled module can be particularly outside of the housing 5 check for their electrical functionality, which in particular a troubleshooting is particularly easy.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10140071 A [0005]
• DE 102009001062 A [0006]
• FR 2876161 A [0007]
• EP 1888910 B1 [0008]

Claims (12)

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 distribution 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 ), - with a fuel through-flow preheat space ( 10 ), from the housing ( 5 ) and which is connected to the inlet port ( 6 ) and with the outlet port ( 7 ) is fluidically connected, - with at least one electrical heating element ( 12 ) for heating the fuel in the preheating space ( 10 ), characterized in that the respective heating element ( 12 ) two outer sides facing away from each other ( 13 . 14 ), on each of which at least one metallic heat transfer body ( 15 . 16 ) arranged in the preheating room ( 10 ) comes into contact with the fuel. Preheating device according to claim 1, characterized in that - on 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 ) with a first contact element ( 19 ) electrically connected to a first heat transfer body ( 15 ) electrically contacted with a first electrical connection ( 13 ) of the respective heating element ( 12 ) is electrically contacted, - that the second electrical connection ( 18 ) with a second contact element ( 20 ) electrically connected to a second heat transfer body ( 16 ) electrically contacted with a second electrical connection ( 14 ) of the respective heating element ( 12 ) is electrically contacted. Preheating device according to claim 2, characterized in that - at least a first heating element ( 12 ) and a second heating element ( 12 ) are provided, - that with the first electrical connection ( 17 ) electrically connected first contact element ( 19 ) a first contact section ( 21 ) and a second contact section ( 22 ), - that the first contact section ( 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 section ( 22 ) of the first contact element ( 19 ) with the first heat transfer body ( 15 ) of the second heating element ( 12 ) is electrically contacted, - that with the second electrical connection ( 18 ) electrically connected second contact element ( 20 ) a first contact section ( 23 ) and a second contact section ( 24 ), - that the first contact section ( 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 section ( 24 ) of the second contact element ( 20 ) with the second heat transfer body ( 16 ) of the second heating element ( 12 ) is electrically contacted. Preheating device according to one of claims 1 to 3, characterized in that - at least one first heating element ( 12 ) and a second heating element ( 12 ) are provided, - that the heat transfer body ( 15 . 16 ) of the first heating element ( 12 ) in one of 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. 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 ) into at least two chambers ( 26 . 27 ) located in one of the inlet port ( 6 ) to the outlet port ( 7 ) leading fuel path ( 28 ) are arranged one behind the other, wherein in each chamber ( 26 . 27 ) at least one such heating element ( 12 ) is arranged. Preheating device according to one of claims 1 to 5, characterized in that the respective heat transfer body ( 15 . 16 ) mutually parallel ribs ( 29 ) which are spaced apart transversely to their longitudinal direction and between flow channels ( 30 ) through which one from the inlet port ( 6 ) to the outlet port ( 7 ) guided fuel path ( 28 ) is passed. Preheating device according to claim 6, characterized in that the ribs ( 29 ) to a preheat room ( 10 ) bounding wall ( 31 . 32 . 33 . 34 ), so that a substantial portion of the fuel path ( 28 ) in the flow channels ( 30 ) parallel to the ribs ( 29 ) runs. 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 face ( 35 ) of the first chamber ( 26 ) arranged first heating element ( 12 ), by the Flow channels ( 30 ) of the heat transfer body ( 15 . 16 ) of the first heating element ( 12 ), from one of the outlet port ( 7 ) facing away from the front side ( 36 ) of the first heating element ( 12 ) to one from the outlet port ( 7 ) facing away from the front side ( 37 ) of the second heating element ( 12 ), through the flow channels ( 30 ) of the heat transfer body ( 15 . 16 ) of the second heating element ( 12 ), from one of the outlet ports ( 7 ) facing end face ( 38 ) of the second heating element ( 12 ) to the outlet port ( 7 ) leads. Preheating device according to one of claims 1 to 8, characterized in that - the housing ( 5 ) a housing opening ( 39 ), through which the respective heating element ( 12 ) in the preheating room ( 10 ), that the housing ( 5 ) a lid ( 40 ) for closing the housing opening ( 39 ), which for the respective heating element ( 12 ) and the heat transfer bodies ( 15 . 16 ) forms a support on which the respective heating element ( 12 ) with 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 ) in the preheating room ( 10 ) is used. Preheating device according to claim 9, characterized in that the lid ( 40 ) Electrical connections ( 17 . 18 ) for supplying the respective heating element ( 12 ) having electrical energy, the respective one with its heat transfer bodies ( 15 . 16 ) on the lid ( 40 ) mounted heating element ( 12 ) independent of the rest of the housing ( 5 ) with these electrical connections ( 17 . 18 ) is electrically connected. Preheating device according to claim 9 or 10, characterized in that on the lid ( 40 ) Holding elements ( 41 ) for fixing the at least one heating element ( 12 ) and / or the heat transfer body ( 15 . 16 ) are formed integrally. Preheating device according to one of claims 1 to 11, characterized in that the respective heating element ( 12 ) is a PTC element whose opposite outer sides of two electrical connections ( 13 . 14 ) of the PTC element.

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