WO1986004390A1 - Electric heating device for preheating the fuel in internal combustion engines, especially diesel engines - Google Patents

Abstract

The screw head (7) of a hollow screw (5), such as are normally used for attaching the fuel feed line (1) to a fuel filter, is bored with a hole and in this bore (14) a conventional glow-plug (15) is installed in such a way that the pin (15) of the glow plug (16) extends concentrically into the longitudenal bore (14) of the hollow screw (5). This modified hollow screw (5) is fitted directly into the filter housing (2) and connected via a control device (40) to an electrical source. To control the heating of the liquid fuel, a temperature probe (12) is fitted in direct thermal contact with the hollow screw (5), so that the temperature sensed by the temperature probe (12) is not dependent on the temperature of the heated fuel. In this way it is ensured at all times that the glow-plug (15) is switched off at the right time, before the liquid fuel can evaporate. By the direct incorporation of the hollow screw (5) in the filter housing (2) and the efficient heat-conductive connection between the glow-plug (15) and the hollow screw (5) on the one hand and the hollow screw (5) and filter housing (2) on the other, not only is the liquid fuel directly heated but also the filter housing (2).

Description

10. Electric heating device for preheating the fuel of internal combustion engines, in particular

Diesel engines

The invention relates to an electric heating device for preheating fuel in a fuel supply system for internal combustion engines, in particular diesel engines, according to the preamble of claim 1.

20 In internal combustion engines which are operated with liquid fuel ^•, in particular in diesel engines, the problem is that the diesel fuel at temperatures below -5 o C jellied by failure of wax crystals and thickens. These wax crystals collect in

25 fuel filters and reduce or prevent the

Fuel supply to the engine.

To alleviate these problems, during the cold

Season of the gas stations usually so-called

30 winter diesel is offered, which is freely flowable through chemical additives down to o -15 ° C. At temperatures below -15 C, however, winter diesel also begins to spoil. By increasing the addition of chemical additives or by mixing the diesel fuel with Noro 35 malbenzin, the fluidity can be maintained even below -15 C, but the engine power is reduced and the engine load is increased. In addition, such additives also increase the pollutant emissions, which are already increased when the internal combustion engine is operating at low temperatures.

From FR-PS 780 834, a special carburetor is known, for example, in which a heating element is arranged, which heats the liquid fuel prior to combustion on optically timale ^{"temperatures.} Since these known Vorrich¬ processing is _applied. In internal combustion engines, the work with carburetors, the problems that occur in particular with diesel vehicles cannot be solved.

There have therefore been proposed various systems through which the liquid fuel is pre-heated prior to delivery to the internal combustion engine at temperatures at which ^'the paraffin separation or thickening certainly does not occur and that are below the evaporation temperature of the liquid fuel. For example, it has been proposed to design the fuel feed line to be heatable. Such a device is known for example from EP 52 945, in which a thin band-shaped resistance heater is introduced into the interior of the fuel supply line between the filter and the tank. Immediately in front of the filter, the fuel supply line opens into a special connection piece, from which the electrical supply line for the resistance heater is led out and which is screwed onto the fuel filter.

A very similar heating device is also known from EP 68 688, in which also the KraftstoffZu¬ line through a special fitting at the force is bolted cloth filter ^', where again the Alloca- tion is provided for a resistance heater protruding into the fuel supply line.

A disadvantage of these heatable fuel supply lines, however, is that the fuel filter or the filter housing is only slightly heated. If, therefore, precipitates have already formed during long standing times at low temperatures, such a heating device fails. In addition, the subsequent installation becomes more complicated and costly, since the entire fuel supply line usually has to be replaced.

Furthermore, for example from DE-ÖS 30 21 282 an electrical heating device for preheating liquid fuel is known which can be used at a suitable point as an intermediate piece in the fuel supply line. In this known electrical heating device for diesel fuel, a heating element extends into a component with an elongated cavity. The fuel to be heated flows through this cavity and is thereby heated by the heating element. In the area of the outlet opening from the component, that is to say at the point at which the fuel is at the highest temperature, a hole is made opposite the outlet opening, which extends into the cavity of the component and is covered by a temperature sensor in the form of a thermostat . The heating element is switched off by this thermostat when the temperature of the fuel exceeds a predetermined level.

A disadvantage of this known device is again that the filter housing is heated only insignificantly, so that such a heating device is useless for the case in which paraffin has already failed in the fuel filter. A similar arrangement is that in US-PS

44 54 841 disclosed pressure control device for fuel supply lines of internal combustion engines to take. The pressure control device known from this publication has a cylindrical heating element which is screwed concentrically into a cylindrical housing, the inner diameter of which is somewhat larger than the outer diameter of the cylindrical heating element. When this intermediate space remaining between the cylindrical heating element and the cylindrical housing flows through, the liquid fuel is heated. This heating element is regulated via a temperature sensor integrated in the cylindrical housing. In this known device, too, the liquid fuel is heated up in front of the filter element, however, as with other known heating devices, it is not possible to heat the fuel filter or the filter housing directly.

Finally, the Bosch company offers a modified diesel filter with an integrated heating device. In this system, the diesel filter is also directly heated, but the complete fuel or diesel filter must be replaced, so that the installation, in particular the subsequent installation, becomes unnecessarily expensive, if not made impossible.

Furthermore, from DE-OS 30 34 730 a device for preventing excretions in liquid fuels at low temperatures is known, from which the invention is based, in which the electric heating element is arranged in the flow direction of the fuel upstream of the fuel filter. A preheater, in which the electrical heating element is arranged, is inserted between the fuel filter and the fuel feed line with a piece of ring hose. The liquid fuel from the The material feed line flows through this preheater and is warmed up by the heating element. A temperature sensor is arranged in the preheater in the flow direction immediately behind the heating element, which detects the temperature of the heated liquid fuel and interrupts the power supply to the electrical heating element when the temperature of the liquid fuel exceeds 45 to 50 ° C.

Since the temperature sensor detects the temperature of the heated fuel and not the temperature of the heating element, there is a risk that the fuel will be partially heated above the boiling point if the fuel flow is disturbed or reduced, and that gaseous fuel will heat up due to the deteriorated heat transfer the temperature sensor is falsified compared to liquid fuel on the temperature sensor the temperature measurement. As a result, the heating element would continue to heat the fuel, possibly causing a gas explosion. To prevent this, as with other known heating devices for liquid fuels, care must also be taken in this system that the liquid fuel is not heated to a temperature which is above its boiling point or its evaporation temperature. The easiest way to achieve this is that the temperature difference between the heating element and the fuel to be heated is not chosen too large. On the other hand, however, to ensure that the flowing liquid fuel is heated to a certain temperature, either the heating surface of the heating element must be increased or the length of time of the liquid fuel in the preheater must be increased. Both measures lead to an enlargement of the preheater, which in turn makes the system more expensive and additionally makes simple retrofitting more difficult, particularly in the case of motor vehicles in there is not always sufficient space in the immediate vicinity of the fuel filter.

The invention has for its object to provide, with relatively simple means, an electrical heating device with a heating power which, compared to the known heating devices, enables more intensive heating of both the fuel and the filter housing.

This object is achieved by the features of claim 1.

Through the use of a conventional glow plug, as is often used in diesel engines for preheating the combustion chamber, which is used in a screw head bore of a hollow screw, as is usually used for connecting fuel lines to filter elements and the engine , and extends in its longitudinal bore, the size of the electrical heating element is minimized. Due to the good heat-conducting connection between the hollow screw and the glow plug inserted into this hollow screw, in addition to the surface of the glow plug, the inner surface of the hollow screw is also available for heating the liquid fuel.

Characterized in that the temperature sensor is in good heat-conducting contact with the banjo bolt and / or the glow plug (15) and / or the ring hose piece (3; 30), the temperature sensor detects a temperature that is not directly dependent on the temperature of the heated fuel depends, but on the temperature of the glow plug. In part-load or full-load operation of an internal combustion engine equipped with such an electrical heating device The cold liquid fuel apparently rinses the glow plug in the hollow screw, cools it and is thereby heated itself. If the fuel supply is reduced, for example when idling, the temperature of the glow plug increases, since the energy supplied electrically to the glow plug is no longer dissipated as quickly. This increase in temperature is transferred to the temperature sensor via the hollow screw, so that the glow plug can be deactivated in good time before the liquid fuel begins to evaporate.

Also, the ^{'Εxplosions-} or fire pin candle by the Glüh¬ is negligible because once a is turfühlers always detected in time to strong heating of the Tempera¬ through the highly thermally conductive connection between the glow plug and temperature probe, and since the fuel supply system of internal combustion engines air-tight or oxygen sealing is completed and • consequently no combustion can take place.

The sub-claims 2 and 3 relate to preferred arrangements of the temperature sensor, so that the temperature detected by the temperature sensor is not directly dependent on the temperature of the fuel.

According to an advantageous further development according to claim 4, the temperature sensor is mounted on a holding part made of a good heat-conducting material, which in turn is in good heat-conducting contact with the banjo bolt. Standard temperature sensors can thus be used, since the temperature sensor does not have to be adapted to the special design of the hollow screw, but rather the holding part can be adapted to the specified configuration of the temperature sensor. In an advantageous development according to claim 5, the banjo bolt is made of hardened copper, whereby the thermal contact between the temperature sensor and glow plug is improved. As an alternative to this, this thermal contact could also be improved in that not the entire banjo bolt is made of copper, that is to say a good heat conductor, but rather that only thermal bridges made of a good heat-conducting material, in particular copper, are provided between the glow plug and the holding part .

In a ^{'particularly} preferred development according An¬ demanding 7, the screw head bore of the hollow screw is provided with a thread, whereby the glow plug can be easily mounted on the one hand and on the other hand a good thermal contact is ensured between the glow plug and the hollow screw.

According to one embodiment of the invention according to claim 8, the holding part is a sealing element between the

Ring hose piece and the screw head or the filter housing formed. A further reduction in size is achieved because one component fulfills two functions.

In a preferred development according to claim 9, the holding part is made of copper, as a result of which the thermal contact between the temperature sensor and the banjo bolt is improved.

In an embodiment of the invention according to claim 10, the temperature sensor is designed as a thermal switch, which are commercially available as inexpensive integrated components of small size, which enables simplified electrical wiring. According to an embodiment according to claim 11, the thermal switch is designed as a fail-safe component, for example by using optocouplers, so that any failure of the thermal switch leads to an open switching state and the power supply to the glow plug is interrupted in the event of any type of fault condition becomes.

In a particularly advantageous development of the invention, the battery of an internal combustion engine is prevented from being additionally loaded in the starting phase, since the performance of a battery is significantly reduced anyway at low temperatures.

The sub-claims 13 and 14 relate to further advantageous refinements of the invention.

• A particular advantage of Vorrichtung- invention ^is' that no additional space is required for installation of the heating element, and that the installation can be performed with minimal structural changes only by the hollow screw on the fuel filter through the inventive hollow screw with the incandescent pen candle is replaced. The changes that have to be made to a conventional banjo bolt are also minimal. It only has to be drilled through the hollow bonnet head and provided with a thread in which the glow plug is then screwed in.

The arrangement of the glow plug inside the

Hollow screw remains a comparatively thin cylindrical annular gap. The fuel to be heated is forced through this annular gap and the entire fuel to be heated is essentially heated by direct contact with a heating surface, while the very slow heating of the fuel molecules to each other hardly plays a role due to heat conduction.

Due to the good heat-conducting metallic connection between the glow plug and the hollow screw and again the hollow screw with the filter housing, the filter housing is also heated by heat conduction, so that paraphin present in the fuel filter is melted if the electrical heating device according to the invention is too late has been switched on, or the motor equipped with it has not been in operation for a long time and has been exposed to low temperatures.

Since many internal combustion engines, especially also diesel engines, have a fuel return through the injection pump into the tank, the liquid fuel in the tank is also heated in this way, so that none in the area between the tank and the electrical heating element temperature- ^related excretions can form more.

The direct thermal coupling of the monitoring temperature sensor with the electrically heated glow plug increases the safety of the electrical heating device considerably, since the switching off of the heating element is guaranteed even when there is no liquid fuel in the immediate vicinity of the glow plug.

Further details, features and advantages of the invention result from the following description of several embodiments with reference to the drawing.

It shows:

1 shows a section of the connection point of the fuel supply line to the fuel filter of the structurally tegrated glow plug, and

Fig. 2 shows a second embodiment of the electric Heiz¬ device, which at any point in the

Fuel supply line can be used, and

3 shows an exemplary electrical circuit of the heating device according to the invention.

The section shown in FIG. 1 shows the connection point of the fuel supply line 1 to a fuel filter housing 2, which is only partially shown. The end of the fuel supply line 1 is plugged onto a commercially available ring hose piece 3 with a connecting nozzle 4, which is connected via a commercially available M 14 banjo bolt 5 is screwed to the filter housing 2. A sealing element 6 in the form of a copper sealing ring is arranged between the ring tube piece 3 and the filter housing 2. Between the ^'screw head 7 of the hollow screw 5 and the annular hose section 3 is arranged an unwound holding member 8 made of copper with a hole 9 having a leg 10 as a sealing member. A temperature sensor 12 in the form of a thermal switch is screwed onto the other leg 11 of the holding part 8 and opens o when a temperature of 40-50 ° C. is exceeded.

The screw head 7 is drilled out centrally so that the inner longitudinal bore 13 of the hollow screw 5 continues outwards in a screw head bore 14. The screw head bore 14 is provided with a thread 21 into which a commercially available single-pole glow plug 15 is screwed so that its glow plug 16, which is provided with an electrical heating coil, is arranged concentrically inside the longitudinal bore 13 and between the wall of the hollow screw 5 and an annular gap remains in the glow plug 16. The inside diameter of the longitudinal bore 13 of a commercially available hollow screw 5 is about 8 mm, the outside diameter of the glow plug 16 of a conventional are about 6 mm, so that an approximately 2 mm wide annular gap remains between the glow plug 16 and the inner wall of the longitudinal bore 13. Electrical energy can be supplied to the glow plug 15 via an electrical conductor 17 which is connected to an electrical connection 18.

The ring hose section 3 has a circumferential channel 19 into which the hose nozzle 4 opens. The hollow screw 5 has a plurality of radial bores 20 in the area in which the annular hose section 3 lies, so that fuel from the fuel supply line via the annular hose section 3, the radial bores 20 enters the longitudinal bore 13 of the hollow screw 5. The glow plug 15 has an electrical heating power of, for example

200 watts, whereby the fuel flowing through the longitudinal bore 13 with the glow plug 16 is heated to about 40 to 60 ° C. • -.

FIG. 2 shows an embodiment of the electrical heating device according to the present invention which can be used at any point in the fuel feed line of an internal combustion engine.

The structure of the hollow screw 5 with glow plug 15 is completely identical to the corresponding parts of the embodiment according to FIG. 1 and these parts are therefore identified by the same reference numerals. The only difference from the embodiment according to FIG. 1 is that instead of an annular hose piece 3 with a connecting sleeve, an annular hose piece 30 with two connecting sleeves 31 and 32 is used, and that the hollow cap 5 with the built-in glow plug 15 does not touch a filter housing, but is screwed into a screw cap 33. The one supplied via a hose end 34

Fuel enters the longitudinal bore through the holes 20. tion 13 with the glow plug 16, is heated there and leaves the longitudinal bore 13 again through the bores 20 and flows through the connecting nozzle 32 of the ring hose piece 30 in a hose part 35 further.

In a manner not shown in detail, the temperature sensor 12 can also be attached to the part of the glow plug 15 protruding from the hollow screw 5 or to the ring tube piece 3 or 30.

3 shows an example of the electrical connection of the heating device according to the invention to the electrical system of a car or truck. A control device 40 has a battery connection 41, an alternator connection 42, a ground connection 43 and a first and second output connection 44 and 45, respectively. The battery terminal 41 is connected to a positive terminal 46 of the Bat¬ terie while the alternator terminal 42 _m a positive voltage terminal 47 leading ei¬ ner alternator not shown is connected. A hand switch 48, a thermal switch 49 and the excitation coil of a relay 50 are connected in series between the alternator connection 42 and the ground connection 43. The load side of this relay 50 is connected once to the battery connection 41 and in parallel to the first and second outputs 44 and 45, respectively. The electrical heating winding 51 of the glow plug 16 is connected between the first output 44 and ground. A control lamp 52 is connected between the second output 45 and ground.

If there is a sufficiently large voltage at the alternator connection 42, ie when the engine is running, the manual switch 48 and the thermal switch 49 are closed, the contacts on the load side of the relay 50 are closed and the glow plug 16 and the associated plug Control lamp 52 are supplied with power in parallel. If the glow plug heats up above a predetermined temperature value of, for example, 45 ° C., for example if less fuel or fuel with a higher temperature flows through the heating device, the thermal switch 49 opens and the switching contacts on the load side of the relay 50 open. The power supply to the glow plug 16 and the control lamp 52 is thus interrupted, so that no further heating ^{'r' of} the liquid fuel takes place.

By connecting the control device 40 to the alternator, it is prevented that the electrical heating device according to the invention is already operated in the start-up phase, since the battery is already heavily loaded anyway and additionally a battery at low temperatures. training temperatures has a significantly reduced performance. To initiate the starting process satisfies a fraction which injection pump between the fuel filter and Ein¬ or located in the moment when the motor starts to rotate, provides in the injection pump located ^"fuel quantity. Alternator current, and the electric heater is put into operation Even if the fuel in the injection pump was already gummed, this would not be particularly disturbing, since injection pumps have a sufficiently high output to deliver fuel that has thickened or gummed up, even if it is in the fuel filter has already eliminated Paraphin, this would melt again quickly due to the good thermal contact between the heating element and the filter housing, so that with the device according to the invention, a diesel engine that is already gummed can be put into operation again without outside help.

All hands are suitable for the purpose according to the invention. usual glow plugs, as they are called

Fast glow plugs can be used for diesel engines. The appropriate glow plug can be selected from the offered glow plugs with different heating capacities, taking into account the supply voltage available, the fuel consumption of the internal combustion engine and the desired heating of the liquid fuel. If required, the desired heating output can also be adjusted accordingly by means of adjustable series resistors.

In the case of gasoline engines of higher power, it may be advantageous to make several screw head bores in the hollow screw 5, in each of which a glow plug is installed. In this way, the increased heat requirement for heating the larger fuel throughput in internal combustion engines with greater power can be introduced in an advantageous manner.

Claims

Claims _Q 1. Electric heating device ^" for preheating fuel in a fuel supply system for internal combustion engines, in particular diesel engines, with at least one tank, a fuel feed pump, - a fuel filter, a fuel feed line, - an electric heating element arranged upstream of the fuel filter and one Control device with a temperature sensor for switching the electrical heating element on or off, wherein the fuel feed line can be screwed into the fuel filter by means of a banjo screw with a longitudinal bore and an annular hose piece that is usually used, characterized in that. that the electric heating element has at least one 5 glow plug (15), which is installed in a screw head bore (14) of the hollow screw (5) and extends into the longitudinal bore (13) of the hollow screw (5) and which is at least partially in direct thermal contact with the hollow screw (5), and that the temperature sensor (12) is in direct thermal contact with the banjo bolt (5) and / or the glow plug (15) and / or the ring hose piece (3; 5 30). 2. Electrical heating device according to claim 1, characterized in that the temperature sensor (12) is arranged on a part of the glow plug (15) which protrudes from the hollow screw (5). 3. Electrical heating device according to claim 1, characterized in that the temperature sensor (12) on the annular tube piece (3; 30) is arranged. 10 4. Electrical heating device according to claim 1, characterized in that the temperature sensor (12) on a holding part (8.) of good heat-conducting material is mounted. 5. Electrical heating device according to one of the preceding claims, characterized in that the hollow screw (5) consists of hardened copper. 6. Electric heating device according to claim 5, characterized 20 characterized in that the hollow screw (5) in the area of the screw head (7) in which the holding part (8) is arranged has radial bores which extend into the longitudinal bore (13) and which have good heat-conducting material, especially copper, aus¬ 25 fills. 7. Electrical heating device according to one of the preceding claims, characterized in that the screw head bore (14) of the banjo bolt (5) with 30 is provided with a thread (21). 8. Electrical heating device according to one of claims 2 to 5, characterized in that the holding part (8) at the same time as a sealing element (10) between the 35 ring hose piece (3) and the hollow screw (5) or the filter housing (2) is formed. 9. Electrical heating device according to one of claims ^• 2 to 6, characterized in that the holding part (8) is made of copper. 10. Electrical Heizvorrichtuήg according to one of the preceding claims, characterized in that the temperature sensor is designed as a thermal switch (12) which opens when a predetermined temperature is exceeded. 11. Electrical heating device according to claim 10, characterized in that the thermal switch (12) is designed as an error-free component. 12. Electrical heating device according to one of the preceding claims, characterized in that the power supply to the glow plug (16) via an electrical line (17) and / or the power supply to the control device (40) is carried out by a generator which is supplied by the Internal combustion engine is driven. 13. Electrical heating device according to one of the preceding claims, characterized in that. the screw head (7) of the hollow screw (5) has a bore (14) which extends into the longitudinal bore (13). 14. Electrical heating device according to one of the preceding claims, characterized in that the Glow plug (16) is inserted in such a way that its glow plug (15) is concentrically spaced within the longitudinal bore (13).