WO2001057384A2

WO2001057384A2 - Fuel injector for diesel fuel

Info

Publication number: WO2001057384A2
Application number: PCT/DE2001/000382
Authority: WO
Inventors: Manfred Ruoff; Gert Lindemann; Heinz Stutzenberger; Juergen Haller; Friederike Lindner; Marc Bareis; Horst Harndorf
Original assignee: Robert Bosch Gmbh
Priority date: 2000-02-01
Filing date: 2001-01-31
Publication date: 2001-08-09
Also published as: DE10004313B4; WO2001057384A3; DE10004313A1

Abstract

The aim of the invention is to provide a device for pre-heating the fuel for the cold start of a diesel powered internal combustion engine that does not require a bulky pencil-type glow plug. To this end, the inventive fuel nozzle is provided with a resistance heating layer (20) that especially consists of a ceramic material and that is disposed in the zone of the flow path of the fuel to be injected.

Description

Diesel fuel injector

State of the art

The invention relates to a diesel fuel injection nozzle which enables preheating of the fuel to be injected, in particular diesel fuel.

In order to enable a cold start of a diesel engine, glow plugs are used in many cases, which protrude into the combustion chamber at a certain point. However, this has turned out to be a hindrance in the course of technical development and in the development of better efficiencies and lower exhaust emissions, since the glow plug significantly interferes with the flow of the combustion gases in the combustion chamber.

The object of the invention is therefore to enable diesel fuel preheating without the need for an annoying glow plug.

Advantages of the invention

A diesel fuel injection nozzle with the features of claim 1 enables preheating of the fuel to be injected immediately before the injection. The resistance heating layer allows the fuel volume that is already inside the injection nozzle to be preheated before the diesel engine starts. This fuel volume is usually sufficient for approximately 3 injection processes. Assuming that this fuel volume heated to around 400 ° C, it reliably enables a cold start of the diesel engine even at low ambient temperatures of, for example, -30 ° C. The fuel volume flowing into the injection nozzle after the engine is started is heated in the same way by the heating layer, depending on the respective operating conditions, either preheating to a temperature value in the order of 400 ° C or preheating to lower temperature is sufficient. By dispensing with the glow plugs in the cylinder head, the technical effort and the installation space in the cylinder head are reduced. Furthermore, the removal of the receiving holes for. the glow plugs to increase the stability and torsional rigidity of the cylinder head.

The resistance heating layer is preferably made of ceramic. In this way, an electrically conductive, high-temperature ceramic heating layer can be formed, which can be arranged on an electrically insulating carrier material. For example, a SiN-based ceramic layer doped with MoSi ₂ can be used to achieve almost any electrical property (specific resistance at 20 ° C, behavior of the resistance over temperature, etc.). With such a ceramic heating layer, such a heating power can be implemented that the fuel volume resting in the injection nozzle before the engine is started can be heated to a temperature of about 400 ° C. in about 5 seconds.

drawings

The invention is described below with reference to a preferred embodiment, which is illustrated in the accompanying drawings. In these show:

- Figure 1 shows a fuel injector according to the invention in a longitudinal section;

- Figure 2a on an enlarged scale the detail II of Figure 1; - Figure 2b shows a section along the plane 11-11 of Figure 2a;

- Figure 3 on an enlarged scale the section III of Figure 1;

- Figure 4a on an enlarged scale the section IV of Figure 1;

- Figure 4b in a view corresponding to that of Figure 4a an alternative embodiment;

- Figure 5a in a view corresponding to that of Figure 4a, a variant of the embodiment shown in Figure 4a;

- Figure 5b in a view corresponding to that of Figure 5a shows a variant of the embodiment shown in Figure 4b;

- Figure 6 on an enlarged scale the section VI of Figure 1; and

FIG. 7 shows a diagram of various characteristic values which are obtained with an injection nozzle according to the invention.

Description of the embodiment

FIG. 1 shows an injection nozzle which contains a nozzle body 10 and a nozzle needle 12 which is displaceably arranged therein as the most important components. The structure and the mode of operation of such an injection nozzle are generally known, so that it is only dealt with here insofar as is necessary to understand the invention.

The fuel to be injected is fed via a supply bore 14 in the nozzle body 10 from the rear side of the injection nozzle, that is to say the side facing away from the combustion chamber, to the front side of the injection nozzle, that is to say the side facing the combustion chamber. In the front area of the nozzle body 10, an annular channel 16 is formed, which is in the area from the front end considered cross-sectional expansion of the nozzle needle 12 is arranged. Starting from the annular channel 16, the fuel to be injected flows along a gap 18 with an annular cross section between the nozzle needle 12 and the nozzle body 10 to the front end of the nozzle body 10, from where it, when the nozzle needle! is lifted from its seat, can be injected into the combustion chamber of the internal combustion engine through spray holes.

The fuel to be injected is preheated by means of a resistance heating layer 20 which, in the embodiment shown, is arranged on the nozzle needle 12 essentially in the region of the gap 18. The resistance heating layer 20 is supplied with current starting from an electrical connection 22 which is in electrically conductive connection with the nozzle needle 12. The resistance heating layer 20 is connected to the nozzle needle 12 in the region of the front end of the nozzle needle. The side of the resistance heating layer 20 facing away from the front end of the nozzle needle 12 is electrically conductively connected to the nozzle body 10 via a contact ring 24 which is arranged in the ring channel 16. The nozzle body 10 represents a ground connection, so that no separate return line is required. This structure is explained in detail below with reference to FIGS. 2 to 6. *

The nozzle needle 12 consists of a metal core 26 and an insulating ceramic coating 28, the thermal expansion of which is matched to the thermal expansion of the metal core 26 of the nozzle needle 12. The resistance heating layer 20 is applied to the insulating ceramic coating 28 in the region of the nozzle needle 12, which is designed with a reduced cross-section and extends from the ring channel 16 to the tip of the nozzle needle. Various compositions are possible for the heating layer 20. The basic requirements are that the heating layer is suitable for resistance heating and tolerates temperatures up to about 1000 ° C. An example of a possible material composition is based on SiN ₄ , which is doped with MoSi ₂ . The heating layer 20 is connected in the front region of the nozzle needle 12 to the electrically conductive metal core 26 in that the metal core with four cross-shaped webs 30 passes through the insulating ceramic coating 28 (see in particular FIG. 2b). At the opposite end, the heating layer 20 is formed with a contact area 32 (see in particular FIG. 3), which is made with a greater wall thickness than the layer thickness in the other areas. The greater wall thickness reduces the resistance present there, so that the heating power is converted in the other areas of the heating layer 20 and the contact area 32 warms up moderately at most.

The electrical connection from the contact area 32 of the resistance heating layer 20 to the nozzle body 10, which represents the ground potential, takes place by means of the contact ring 24, which is arranged in the ring channel 16. The contact ring 24 (see in particular FIG. 3) is preferably provided with three contact tabs 34 which are bent back by almost 180 ° at their free end, so that a nose 36 is formed. Thus, a resilient movement in both the radial and axial directions is possible at the free end of the contact tabs 34, so that the lugs 36 can follow the opening stroke and the closing stroke of the nozzle needle 12 of approximately 0.25 mm, without any relative movement between the lugs 36 and the contact area 32 of the heating layer 20 occurs. There is preferably static friction, so that premature wear of the contact area 32 is prevented. In order to prevent rotation of the contact ring 24 in the ring channel 16, which could lead to the supply bore 14 to the ring channel being covered by one of the contact tabs, the contact ring 24 is provided with a locking tab 38, the free end of which is bent outward in the radial direction so that it engages in an extension 40 of the feed bore 14.

The contact tabs 34 and the locking tab 38 are connected to one another by a connecting tab 42 which is arranged on the side of the annular channel 16 facing the gap 18. The connecting tab 42 is provided with a slot 44 immediately next to the locking tab 38. ^* The slot makes it possible to insert the contact ring 24 into the ring channel 16 with a clamping effect. The contact ring 24 consists of a resilient, electrically highly conductive material and can be punched out of a metal sheet. Suitable materials are, for example, CuCrZr F49, CuNi2 Si F51 or CuNi18Zn20 F58. These materials can be used up to a temperature of 450 ° C without exceeding the R 0.2 limit. The suitable pre-bent contact ring 24 is stamped out for assembly by pushing the slot 44 together so that it can be inserted into the annular channel 16 through the gap 18 starting from the front end of the nozzle body 10. There, the contact ring 24 will spring back into its starting position, and the locking tab 38 protrudes toward the extension 40 of the feed bore 14. Finally, the free end of the locking tab 38 can be bent into its final shape using a suitable tool which is inserted into the feed bore 14.

By arranging the slot 44 in the vicinity of the locking tab 38, the fuel flowing from the supply bore 14 through the annular channel 16 into the gap 18 is disturbed as little as possible. Due to the enlargement of the flow cross-section caused by it, the slot 44 also leads to favorable pressurization by the flowing fuel. Since a higher static pressure occurs in a flow in the areas in which the flow cross section is larger than in areas with a smaller flow cross section, a slightly higher static pressure acts on the end faces of the connecting plate 42 there than on the other peripheral areas the connection tab. Thus, compressive forces act there in the circumferential direction, which press the connecting lug 42 against the wall of the annular channel 16 in addition to the otherwise existing radial spring force.

The free, bent end of the locking tab 38, which engages in the extension 40 of the feed bore 14, is preferably supported on the wall of the extension 40 in such a way that a ramp is formed by the free end, which is the ramp from the feed bore 14 into the annular channel 16 incoming fuel deflected appropriately. In this way it is prevented that the fuel flow animal tab 38 sucks into the interior of the ring channel 16 and then attacks on the back of the locking tab 38 so that it can be bent or even destroyed.

The fuel flowing in the annular channel 16 also exerts pressure forces on the locking tabs 34, which are favorable for operation. A relatively slow fuel flow results in the area of the lugs 36, so that the static pressure there is greater than further down in the annular channel 16 towards the gap 18. As a result, the lugs 36 are subjected to a compressive force with respect to FIG. 3 from top to bottom. Since the lugs 36 are located radially further inward than the end of the contact lugs 34 connected to the connecting lug 42, there is a leverage effect, so that the lugs 36 are urged inwards against the contact region 32.

The electrical connection from the connection 22 to the electrically conductive metal core 26 of the nozzle needle 12 is made by a connecting conductor in the form of a cable 46 which is connected to the rear end of the nozzle needle 12. For this purpose, a conical receptacle 48 (see in particular FIG. 4a) in the manner of a centering bore is formed in the metal core 26 at the rear end of the nozzle needle 12.

The cable 46 is provided with a connection end 50 assigned to the nozzle needle 12, which is designed as a cone in the embodiment shown in FIG. 4a. The cone is pressed into the receptacle 48 by a spring plate 52, on which a return spring 54 for the nozzle needle is supported. The spring plate 52 in this embodiment consists of electrically insulating ceramic, so that the metal core 26 of the nozzle needle is electrically insulated from the return spring 54 and the nozzle body 10, on which the other end of the return spring is supported.

The conical connecting end 50 is dimensioned such that the high spring forces of the return spring 54 deform it slightly plastically after assembly, but the spring plate 52 directly at the end of the spring assigned to it Metal core 26 of the nozzle needle rests so that the functional forces of the return spring 54 are not falsified by a change in the spring travel. The remaining elastic tension in the connection end during the plastic deformation of the conical connection end 50 ensures that the connection end 50 always maintains good metallic contact with the receptacle 48 during operation of the injection nozzle, so that the electrical contact from the cable 46 to the heating layer 20 is ensured.

FIG. 4b shows a variant of the embodiment shown in FIG. 4a. The only difference is that the connection end 50 is designed here as a slotted ring, so that there is a greater spring travel with lower spring forces.

FIG. 5a shows an alternative embodiment to the design shown in FIG. 4a. The spring plate 52 is made of steel for reasons of cost and is provided with an insulating sleeve 56 made of electrically insulating ceramic along its central opening. The insulation sleeve 56 is provided with a shoulder which bears against a corresponding shoulder of the spring plate. The insulation sleeve can thus transmit the required compressive forces to the connection end 50 of the cable 46. At the same time, electrical insulation is guaranteed in this area.

FIG. 5b shows the configuration of the spring plate known from FIG. 5a in combination with the configuration of the connecting end 50 of the cable 46 known from FIG. 4b.

The cable 46 extends from its connection end 50 upwards to the electrical connection 22, it being inserted so loosely that it can easily follow the opening stroke and the closing stroke of the nozzle needle. In the area of the end of the return spring 54 which is supported on the nozzle body 10, a support disk 58 and a protective grommet 60 are provided, which serve to mechanically protect the cable 46. In addition, a thickened protective lacquer could be provided on the cable 46, which would cause a bright rubbing in the area the return spring 54 is to prevent. Furthermore, a protective tube or a shrink tube could be pulled onto the cable 46. Due to the operating temperatures prevailing in this area of the injection nozzle, plastic or rubber are suitable as materials.

After passing through the protective grommet 60, the cable 46 is bent at a right angle and passes through a sealing part 62. The sealing part 62 can, for example, consist of a thermoplastic material and serves to seal the passage of the cable 46 to the outside of the nozzle body 10, since leakage fuel is present in this area. The sealing part 62 is biased by a clamping screw 64 so that the desired tightness is obtained. The electrical connection 22 is then arranged outside the tensioning screw 64 and can be suitably designed with regard to the required contacting of the cable 46.

Deviating from the embodiment shown in the figures, it is fundamentally also possible to form the resistance heating layer in the area of the gap 18 on the inner wall of the nozzle body 10 in order to preheat the fuel to be injected in this area.

FIG. 7 shows a diagram which shows the temperature of various components of the injection nozzle during the preheating of the fuel and the power expended for it. The curves shown are based on a simulation for an injection nozzle, in which the resistance heating layer is arranged on the inner wall of the nozzle body 10. Regardless of the specific values, the following general knowledge can be obtained: The temperature of the fuel in the gap 18 increases to around 400 ° C. over a period of 5 seconds (see curve T18). During this time, the heating layer 20 heats up to a temperature of slightly above 700 ° C (see curve T20). The temperature of the nozzle needle 12 rises only slightly to about 100 ° C. (see curve T12). The power implemented in the process drops from an initial value of approximately 200 watts to less than 40 watts within the first second; then it continues to decrease with a slight incline (see curve P46 for the power supplied through cable 46 and curve I46 for the current flowing in cable 46). Since the power transmitted by the cable 46 drops to about a third of the starting value within a tenth of a second, it is possible to work with comparatively small cross sections.

If the heating layer is operated for a longer period of time, temperature values which are undesirable would result after a period of operation of about 7 seconds. For example, the nozzle needle would heat up to over 180 ° C, the fuel would have a temperature of over 450 ° C, and the heating layer would heat up to temperatures of over 950 ° C. Temperature control is therefore required. This could be done, for example, by control electronics that use the flowing electrical current as a temperature measurement. Similar to the temperature control in a glow plug, it is also possible to divide the total resistance into a pure heating resistor and a control resistor similar to the control coil in a glow plug. Then a control unit similar to the control unit currently used for a glow plug could be used.

When the fuel is heated to a temperature of around 400 ° C, it is already at or slightly above the boiling point. Thus, at least the boiling pressure must be present in order to prevent outgassing, since a boiling or outgassing fuel in the area of the gap 18 in front of the spray holes of the nozzle body 10 would have negative effects on the injection. The required boiling pressure can either be built up in that the inlet bore 14 and the other supply lines for the fuel at the temperatures at which fuel preheating is required exert such throttling resistance on the fuel which is sultry or viscous at these temperatures in that a certain back pressure builds up when heated. It is also possible to provide a check valve that prevents expansion of the fuel in the nozzle body during preheating. This check valve should be designed with the largest possible opening cross-section so as not to hinder the fuel supply during operation.

Claims

claims

1. Injection nozzle for an internal combustion engine, in particular for diesel fuel, with a resistance heating layer (20) which is arranged in the region of the flow path (18) of the fuel to be injected.

2. Injection nozzle according to claim 1, characterized in that the heating layer (20) consists of ceramic.

3. Injection nozzle according to one of claims 1 and 2, characterized in that the injection nozzle has a nozzle needle (12) and the heating layer (20) is arranged on the nozzle needle.

4. Injection nozzle according to claim 3, characterized in that the injection nozzle has a nozzle body (12) surrounding the nozzle body (10) and that the nozzle body is provided with a contact ring (24) which bears against a contact region (32) of the heating layer.

5. Injection nozzle according to claim 4, characterized in that the contact ring (24) is arranged in an annular channel (16) at a distance from the front end of the injection nozzle.

6. Injection nozzle according to claim 5, characterized in that the contact ring (24) is provided with a plurality of contact tabs (34) which abut the contact region (32) of the heating layer, and with a locking tab (38) which in a fuel supply bore (14) engages in the nozzle body.

7. Injection nozzle according to one of claims 3 to 6, characterized in that the nozzle needle! (12) from a metal core (26) and an insulating ceramic Coating (28) is that the heating layer (20) is arranged on the insulating ceramic coating and that the heating layer is in electrical contact with the metal core in the region of the front end of the nozzle needle ¹ (12).

8. Injection nozzle according to one of claims 3 to 7, characterized in that the nozzle needle (12) is provided at its rear end with a conical receptacle (48) and that a connecting conductor (46) is provided which has a connecting end (50) is provided, which is pressed into the receptacle in the rear end of the nozzle needle by a spring plate (52) on which there is a return spring (54) for the nozzle needle! (12) supports.

9. Injection nozzle according to claim 8, characterized in that the connection - end is designed as a cone (50).

10. Injection nozzle according to claim 8, characterized in that the connection, end (50) is designed as a slotted ring.

11. Injection nozzle according to one of claims 8 to 10, characterized in that the spring plate (52) is provided with an insulation sleeve (56) so that the connection end (50) against the return spring (54) and thus the nozzle body (10) insulates is.

12. Injection nozzle according to one of claims 8 to 10, characterized in that the spring plate (52) consists of insulating ceramic, so that the connection end (50) with respect to the return spring (54) and thus the nozzle body (10) is isolated.

13. Injection nozzle according to one of claims 1 and 2, characterized in that ^' the injection nozzle has a nozzle body (10) which surrounds a nozzle needle (12), and that the heating layer (20) is arranged on an inner surface of the nozzle body (10) ,

14. Injection nozzle according to one of the preceding claims, characterized in that the nozzle body (10) consists of insulating ceramic.