GB2099321A - Fuel feed system - Google Patents

Abstract

A fuel feeding system for an internal combustion engine, in particular a compression-ignition or Diesel engine comprises a filter (5) and a fuel pump (3) which may also have a filter (4). Heating element(s) (13, 14) are provided within the filter element of the or each filter (4, 5) for partially melting waxy or paraffin fuel deposits therein, and the or each heating element (13, 14) extends over only a part of the surface area of the respective filter element for instance over 5 to 50 percent of said surface. A further filter (7) may be associated with the fuel supply tank (1), this filter also being provided with a heating element (15). The system is particularly suitably for operation of the internal combustion engine in low temperature conditions and reduces the drain on the vehicle battery when starting up while simultaneously melting any fuel deposits tending to block the fuel feed system. <IMAGE>

Description

SPECIFICATION Fuel feed system The invention relates to a fuel feed system for an internal combustion engine, for example for diesel fuel, in an air-compressing, fuel-injected or "Diesel" engine.

It is generally known that at low environmental temperatures, waxy or paraffin deposits clogging up the filter surfaces and other narrow passages in the conveying path form in certain fuels, in particular in diesel fuel.

The lowtemperature behavior of fuels is adapted by the mineral oil companies to the climatic conditions under which the fuels are to be used by the selection of appropriate components. Austraian Standard C 1104 defines the lowtemperature behavior of a diesel fuel exclusively according to the so-called "cold filter plugging point" (CFPP) and establishes this value with a maximum of + 5"C for the summer (April 1 through September30) and a maximum low temperature of - 1 5"C for the winter (October 1 through March 3).The cold filter plugging point is determined in a standard apparatus by measuring that temperature at which a predetermined ammount of the fuel cooling in a refrigerating brine can no longer be sucked through a screen of standard mesh size at predetermined vacum or reduced pressure within a predetermined period of time. This value is intended to indicate possible failures due to waxy or paraffin deposits in pipeline systems and filter screens.

For reasons of economy, the standardization of the low temperature behavior can of course not be adapted to occurring minimum temperatures, so that in certain cases, difficulties arise even if the standard values are observed, as practice has proven time and again.

A known arrangement of the type initially mentioned is provided with a filter having a heatable filter surface. The heating element in the form of an electric resistance wire extends over the entire filter surface so that the entire filter surface is heated. The energy requirements of this filter are so high that they cannot be met in a vehicle without relying on an external energy source. Moreover, the battery efficiency of a vehicle drops so low at low temperatures that there is hardly enough energy left to heat up the entire energy stream flowing through the filter. (U.S.

Patent Specification No. 2 635 174).

It is the object of the invention to reduce the energy requirements for heating the fuel with simultaneous maintenance of the conveyance of the fuel.

According to the invention, there is provided a fuel feed system conveying fuel to an internal combustion engine, said system comprising at least a pipe means and a filter means with at least one heating element provided in the conveying path of the fuel within the filter surface of the filter, wherein said heating element extends over only a part of the filter surface, for the purpose of at least partially melting waxy or paraffin deposits of the fuel in the filter.

This measure allows a partial heating of the filter surface or another critical spot in the conveying path of the fuel quickly and with low energy expenditure at and following the cold start of the machine at low outside temperatures, so as to eliminate a possible obstacle in the conveying path of the fuel caused by waxy deposits.

The result is a melting of the wax or paraffin on a limited filter surface which merely requires raising the temperature of a limited filter surface above the melting point of the deposit, but not heating beyond that, let alone heating up the entire fuel stream flowing through. This permits an essentially reduced energy requirement so that the amount of energy needed may be drawn from a vehicle battery even at low temperatures without impairing the starting efficiency.

The required time of operation of the heating element for rapid heating is assured by the fact that the heating element of the filter can be controlled or regulated, preferably by means of a time relay, as a function of time. It would of course also be possible to switch the heating element off and on manually.

Embodiments of the invention will now be described in greater detail, by way of example and with reference to the accompanying drawings; in which: Fig. 1 shows a diagram of a fuel feed system according to the invention; Fig. 2 shows the main filter from the installation of claim 1 in enlarged, perspective view; Fig. 3 shows a filter for a fuel pump; Fig. 4 shows a fuel pump with a water collector and a filter and Fig. 5 shows a detail taken from Fig. 4 on an enlarged scale.

The arrangement for conveying diesel fuel from a fuel tank 1 to the injection pump 2 of a Diesel motor (not described in detail) essentially comprises a fuel pump 3 connected to the injection pump 2 of the Diesel motor and driven by this pump and provided with a pre-filter4 and a main filter 5 in the conveying path of the fuel between the fuel pump 3 and the injection pump 2.

The fuel pump 3 sucks in the fuel through a suction line 6 and a coarse filter7 inserted in the container 1, it then forces the fuel through a pressure line 8 to the main filter 5 and further to the injection pump 2.

From the injection pump 2, the fuel is conveyed in a known manner along injection lines 9 to the injection nozzles 10 of which one of each is shown. From the main filter 5, a bypass line 11 leads back to the fuel tank 1. A pressure valve 12 is provided in the bypass line 11, this valve is adjusted to the prepressure required for the injection pump. In order to economise in the heating efficiency of the filters, the valve 12 or another valve in the bypass line 11 can be closed during the starting and warmup operation.

The pre-filter4, the main filter 5 and the coarse filter 7 are each provided with a respective heating element, 13, 14 and 15. The electrically heatable heating elements are arranged in an electric circuit 16 and can be switched on by means of a switch 17 which is actuated by a temperature sensor provided in the pressure line 8 between the main filter 5 and the injection pump 2.

As shown in detail in Fig. 2, the heating element 13 of the main filter 5 has the form of an electric resistance wire embedded or woven into the filter surfaces of the star-shaped filter insert 8. The heating element 13 extends over only a portion of the filter surface.

Fig. 3 shows as a variant to this, an embodiment in which a heating element 19 is wound in the form of an electric resistance wire and a cylindrical filter insert 20. This element also extends over only a portion of the filter surface.

Fig. 4 is an elevation of a fuel pump which has a filter bowl in which a filter insert 22 is enclosed in a metal casing 23.

Fig. 5 shows an enlarged part of the pump of Fig ure4 with a heating element 21 in the form of an electric resistance wire guided around the cylindrical filter insert 22 in three coils. The free end of the heating element 21 is grounded on the interior of the metallic filter casing 23, the otherwise bare, i.e. noninsulated, wire is electrically insulated from the metallic filter casing 23 by means of an insulating sleeve 24 where it passes through the casing. It would of course also be possible to use insulated resistance wires.

Depending upon the operating conditions, in particular the outside temperatures, at which the motor is to be started, the heating elements extend over preferably between 5 and 50 percent of the filter surface in order to assure a partial, rapid melting of the waxy or paraffin deposit with the minimum energy requirement.

The system according to the invention thus makes it possible to employ electricity for melting certain zones in critical surfaces of the filter, in particular the filterscreen ofthefuel pump.

Since this is not a question of heating a large volume of fuel, but merely of melting wax or paraffin in small, limited zones, the energy requirement is extremely low and can be covered by the battery without any problem. Tests have shown that 30 watts distributed over an annular surface of about five square centimeters already constitute an adequate dimension and cause an instant clearance of the fuel passage which has been completely blocked by paraffin.

The invention is mainly intended for devices for conveying diesel fuel, but it may also be applied to devices for conveying other types of fuels inclined to the formation of waxy or paraffin deposits, such as certain types of fuel oil for heating purposes.

Claims (8)

1. A fuel feed system for conveying fuel to an internal combustion engine, comprising at least one pipe means and one filter means, with at least one heating element provided in the conveying path of the fuel within the filter surface of the filter, wherein said heating element extends over only a part of the surface area ofthe filter.

2. A system according to claim 1, wherein the or each heating element extends over between 5 and 50 percent of the surface area of the associated filter insert.

3. A system according to claim 1 or claim 2, wherein the or each heating element is electrically heatable.

4. A system according to any one of the preceding claims, wherein the or each heating element associated with a respective filter can be controlled by means of at least one time relay as a function of time.

5. A system according to any one of the preceding claims, wherein the filter element is star-shaped.

6. A fuel feed system according to claim 1, wherein a pre-filter, a main filter and a fuel pump are provided, each of the said filters having a electrically heatable heating element provided in the conveying path of the fuel within the filter surface of the respective filter, each said electrically heatable heating element extending over only a part of the surface area of the respective filter insert.

7. A fuel feed system according to any one of the preceding claims, wherein diesel fuel is conveyed to a Diesel engine.

8. A fuel feed system substantially as hereinbefore described with reference to and as shown in the accompanying drawings.