GB1587592A

GB1587592A - Fuel system

Info

Publication number: GB1587592A
Application number: GB828978A
Authority: GB
Original assignee: SCHOENEBECK DIESELMOTOREN
Current assignee: SCHOENEBECK DIESELMOTOREN
Priority date: 1977-03-07
Filing date: 1978-03-02
Publication date: 1981-04-08
Also published as: CS247603B1; DD130166B1; FR2383318A1; DD130166A1; HU177187B; FR2383318B1

Description

(54) FUEL SYSTEM (71) We, VEB DIESELMOTORENWERK SCHÖNEBECK, of 33 Schnebeck/Elbe, Barbarastrasse 9, German Democratic Republic, a corporation organised under the laws of the German Democratic Republic do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a fuel system for a compression-ignition internal combustion engine such as a diesel engine.

Known fuel systems have the disadvantage that they are not free of underpressure and not substantially free of secondary air. These disadvantages are due to the fact that fuel columns in fuel suction and return ducts generate an underpressure when the engine is not operating and fuel ducts which are not hermetically sealed permit intrusion of secondary air into the fuel system during extended periods when the engine is not being operated.

US PS 3 125 084 discloses an electrical conveying pump for shortening the phase of preliminary pumping. As a result of high cost, insufficient reliability and limited life due to frequent starting operations and overloading, electrical conveying pumps have disadvantages.

German Federal Republic PS 1 751 275 discloses apparatus in which an auxiliary tank is associated with a mechanically driven two-stage fuel conveying pump to assure, immediately on starting, an adequate fuel supply from the auxiliary tank. The auxiliary tank collects fuel vapour bubbles, absorbs excess fuel from the injection pump and receives a return duct which, for the generation of a slight excess pressure in the auxiliary tank, has a throttle so that possible evaporation is delayed. This arrangement of fuel ducts is designed specially for oper ation with fuels which boil at relatively low temperature and not for air-compressing internal combustion engines which are operated with fuels which boil at higher temperatures.

German Democratic Republic PS 194 310 discloses two mechanically driven fuel conveying pumps and an auxiliary tank so coupled that the two fuel conveying pumps mutually support each other during the starting operation. This has the disadvantage that underpressure formation in the fuel system can not be prevented on extended periods of non-operation of the engine.

According to the present invention there is provided a fuel system for a compressionignition internal combustion engine, comprising two fuel conveying circuits, one of the circuits comprising a main fuel tank, an auxiliary fuel tank disposed above the main fuel tank, fuel feed duct means including a pump for the passage of fuel from the main fuel tank to the auxiliary fuel tank, and a fuel return line disposed in use to communicate a space above the fuel in the auxiliary fuel tank with atmosphere through a space above the fuel in the main fuel tank, the fuel return line having an internal cross-section greater than that of the fuel feed duct means and having a substantially constant inclination, and the other circuit comprising the auxiliary fuel tank, fuel injection means, and another duct means for the passage of fuel between the auxiliary fuel tank and the fuel injection means.

The system may comprise further duct means for conveying fuel under gravity to glow plug means when starting the engine.

The system may comprise throttle means for regulating the flow of fuel when starting the engine.

The system may comprise magnetically actuable value means within the further duct means for controlling the flow of fuel therethrough.

The throttle means may comprise throttles each disposed within the further duct means directly upstream of a respective glow plug.

The throttle means may comprise throttles each disposed within a respective glow plug.

By ventilating the auxiliary tank, the equivalent is obtained of the basic function of a customary fuel tank disposed high and from which the fuel is sucked by a conveying pump.

The minimum inclination of the fuel return line (preferably above 10%) is so chosen that at desired inclinations of a working machine driven by the engine, both when it is being opened and when it is not, a downward gradient in the direction of the main fuel tank is present along all the line sections so as to secure a continuous fuel return flow. The cross-section of the fuel return line is preferably more than double the cross-section of the fuel feed duct means and is so chosen that during the operation of the engine ventilation of the auxiliary tank takes place with pressure equalisation towards the main tank through the return line even with fuel flowing back through the return line.

The opening of the fuel return line into the main fuel tank takes place in the air space above the fuel level, which is preferably connected through a ventilation opening with the surrounding atmosphere.

Furthermore, the fuel feed to the glow plugs is preferably assured by gravity fed fuel flowing through a throttled feed duct during non-operation of the engine and pumped fuel during operation of the engine, preferably flows to the magnetic passage valve for the supply of the glow plugs.

While the gravity fed fuel, flowing to the glow plugs at standstill of the engine and on opening the magnetic valve, is adequate for the formation of an initial ignition, the fuel required increases during turning-over of the engine by the starter and in the initial phase of the self-running of the engine, is fed under pressure to form a stable flame on actuation of a conveying pump. Throttles arranged upstream of the glow plugs regulate the quantity of fuel held within required limits.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawing, the single figure of which schematically shows a fuel circuit for a compression-ignition engine.

An outer fuel circuit comprises a main fuel tank 1 provided with a ventilation opening 2, a coarse fuel filter 3, a fuel conveying pump 4 and an auxiliary fuel tank 5. These components are connected by a suction duct 6 and a conveying duct 7, which preferably have a small cross-section depending on the volume conveyed. A fuel return line 8 having a constant inclination along all its length and having more than twice the cross-section of the conveying duct 7, provides an atmospheric connection between an air space Sa of the auxiliary tank 5 and the space la of the fuel tank 1.

An inner fuel circuit comprises the auxiliary fuel tank 5, a conveying pump 9, a fuel input filter 10, an injection pump 11 and an overflow valve 12. These components are connected by a suction duct 13 with a suction tube 13a, a conveying duct 14 and an overflow duct 15. The fuel supply system of a starting aid is branched from this inner fuel circuit. This system of the starting aid comprises a magnetic valve 19, one or more glow plugs 20, a fuel short-circuit duct 21, a throttle 22, a feed duct 25 and throttles 24. Gravity fed fuel flows from the auxiliary fuel tank 5 at standstill of the engine and additionally through branched-off fuel duct 23 and throttle 26 during operation of the engine.

The throttles 22 and 24, which are matched, determine the metering of the gravity fed fuel during preliminary glowing of the plugs 20. The throttles 24 may expediently be arranged immediately in front of the glow plugs to fill the ducts 25 up as rapidly as possible during preliminary glowing after emptying or partial emptying.

Fuel is sucked from the main fuel tank 1 through the feed duct 6 and the coarse fuel filter 3 by the fuel conveying pump 4 and conveyed through the feed duct 7 into the auxiliary tank 5 disposed highest. The return line 8 is inclined at about 10% from the auxiliary tank 5 towards the main tank 1 and preferably has twice the cross-section of the feed duct. The tank 1 is so connected with the free atmosphere by an opening that during the operation of the first conveying pump, ventilation is assured through the return line 8 even with fuel flowing back to the tank 1. The fuel return line 8 opens into the air space above the level of the fuel in the tank 1. Compared with direct ventilation from the auxiliary tank 5 to the atmosphere, this indirect ventilation has the advantage that temporary overflowing of the auxiliary tank 5 and an ingress of dust and other pollutions is prevented. The injection pump 11 is supplied from the auxiliary tank 5 through the suction tube 13a, suction duct 13, the fuel input filter 10 and the conveying duct 14.

Feeding of an injection nozzle 17 takes place in a known manner. Excess fuel is passed back into the auxiliary tank 5 through the return ducts (overflow duct 15, leakage fuel duct 18). Pressure fuel for feeding the glow plugs 20, is branched off in front of the injection pump.

For fuel supply in the preliminary glowing period, gravity fed fuel flows to the glow plugs through the fuel short-circuit duct 21 and throttle 22. The magnetic valve 19 and the glow plugs 20 are set into operation by a common electrical glow starter switch. Thereby, an initial flame may be developed before actuation of the engine starter so that stable flame development occurs on actuation of the starter and stabilisation of the self-running of the engine is made possible.

Advantages of the embodiment described above by way of example are that it has a high readiness to start at low temperatures and the formation of underpressure is prevented. This is especially the case in fuel systems in which the fuel level in the main tank is at a lower level than the glow plugs.

The fuel system may be used in connection with such plants, machinery or vehicles as automotive agricultural machines, automotive rotary cranes, dredgers, and stationary engines.

WHAT WE CLAIM IS: 1. A fuel system for a compressionignition combustion engine, comprising two fuel conveying circuits, one of the circuits comprising a main fuel tank, an auxiliary fuel tank disposed above the main fuel tank, fuel feed duct means including a pump for the passage of fuel from the main fuel tank to the auxiliary fuel tank, and a fuel return line disposed in use to communicate a space above the fuel in the auxiliary fuel tank with atmosphere through a space above the fuel in the main fuel tank, the fuel return line having an internal cross-section greater than that of the fuel feed duct means and having a substantially constant inclination, and the other circuit comprising the auxiliary fuel tank, fuel injection means, and another duct means for the passage of fuel between the auxiliary fuel tank and the fuel injection means.

2. A system as claimed in claim 1 comprising further duct means for conveying fuel under gravity to glow plug means when starting the engine.

3. A system as claimed in claim 2, comprising throttle means for regulating the flow of fuel when starting the engine.

4. A system as claimed in either claim 2 or claim 3, comprising magnetically actuable valve means within the further duct means for controlling the flow of fuel therethrough.

5. A system as claimed in either claim 3 or claim 4, wherein the throttle means comprise throttles each disposed within the further duct means directly upstream of a respective glow plug.

6. A system as claimed in either claim 3 or claim 4, wherein the throttle means comprise throttles each disposed within a respective glow plug.

7. A fuel system substantially as hereinbefore described with reference to the accompanying drawing.

8. A compression-ignition engine comprising the fuel system as claimed in any one of the preceding claims.

9. A plant, machine or vehicle comprising the engine as claimed in claim 8.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. stabilisation of the self-running of the engine is made possible. Advantages of the embodiment described above by way of example are that it has a high readiness to start at low temperatures and the formation of underpressure is prevented. This is especially the case in fuel systems in which the fuel level in the main tank is at a lower level than the glow plugs. The fuel system may be used in connection with such plants, machinery or vehicles as automotive agricultural machines, automotive rotary cranes, dredgers, and stationary engines. WHAT WE CLAIM IS:

1. A fuel system for a compressionignition combustion engine, comprising two fuel conveying circuits, one of the circuits comprising a main fuel tank, an auxiliary fuel tank disposed above the main fuel tank, fuel feed duct means including a pump for the passage of fuel from the main fuel tank to the auxiliary fuel tank, and a fuel return line disposed in use to communicate a space above the fuel in the auxiliary fuel tank with atmosphere through a space above the fuel in the main fuel tank, the fuel return line having an internal cross-section greater than that of the fuel feed duct means and having a substantially constant inclination, and the other circuit comprising the auxiliary fuel tank, fuel injection means, and another duct means for the passage of fuel between the auxiliary fuel tank and the fuel injection means.

9. A plant, machine or vehicle comprising the engine as claimed in claim 8.