GB2255373A - Diesel engine fuel injection system. - Google Patents

Description

557- A 1 - A fuel iniection device D E S C R I P T 1 0 N The invention

relates to a fuel injection device for diesel engines according to the preamble of the independent claim 1.

"Technische Unterrichtung" [= Technical Information] by Bosch (Diesel Injection Pumps, Types PE and PF; VDT-U 2/1 De) discloses an injection pump driven by a diesel engine and adapted to be connected to an injection nozzle via an injection line at the high-pressure end. The injection nozzle known from the citation also has an overflow-oil line connection. To maintain a constant pressure in the injection line, the known injection pump contains a nonreturn valve and a reverse-flow valve, and at the end of delivery the non-return valve is closed by spring force and the high-pressure system is relieved via the reverse-flow valve. This known fuel injection device has the disadvantage that the high pressure in the injection line fluctuates very widely, owing to changes in the temperature of the engine. This results in uncontrolled variations in the amount of fuel injected through the injection nozzle. This is particularly disadvantageous when the high-pressure volume is large.

The aim of the invention is to provide a diesel-engine fuel injection device which avoids the aforementioned disadvantages.

To this end, according to the invention, a valve is provided in the highpressure region and is connected between the high-pressure region and an overflow-oil line of the injection nozzle and is disposed in the region of the injection nozzle.

The advantage of disposing the valve near the injection nozzle is that the high-pressure volume in the injection line is reduced by discharging through a valve. the high-pressure volume through the valve is an advantageous way of eliminating temperature fluctuations, more particularly in the engine or the fuel. To this end Discharging the valve connected between the high-pressure region and an overflow-oil line of the injection nozzle is a discharge valve. This ensures that the high-pressure volume in the discharge line is reduced by discharging pressurised fuel through the discharge valve into the overflow-oil line. Since the valve according to the invention is positioned so as to reduce the temperature of the high-pressure volume, the pressure in the injection line can also be increased.

If the discharge through the valve occurs against a sufficiently low pressure in the overflow-oil line of the injection nozzle, vapour bubbles are advantageously prevented from forming in the injection line. In addition, some components, more particularly the reverse-flow valve, of the known fuel injection device are no longer necessary, so that the construction is simpler and less expensive.

According to another feature of the invention, the highpressure volume is discharged through the discharge valve and over a control edge disposed in known manner in the injection nozzle.

According to another feature of the invention, the valve is disposed between the injection line and the overflow-oil line of the injection nozzle. The advantage of this arrangement is that commercial injection nozzles can be used and the valve can be subsequently adapted to the construction and operating conditions.

According to another feature of the invention the valve is incorporated in the injection nozzle. This has the advantage that internal combustion engines can be retrofitted by replacing the already-incorporated injection nozzle by a nozzle in which the valve is integrated, thus avoiding temperature problems.

According to another feature of the invention the valve has a restrictor. The restrictor can e.g. be in the form of a constriction in the valve passage, to ensure a defined rate of discharge of fuel into the overflowoil line. In addition, as a result of the restrictor in the valve, the pressure can be reduced to a level above that in the overflow-oil line, in order to maintain a defined pressure level in the injection line.

Preferred embodiments of the invention will now be described in detail with reference to the drawings, in which:

Fig. 1 shows a fuel injection device according to the invention, in which the valve is disposed between the injection line and the overflow-oil line; Fig. 2 shows a fuel injection device according to the invention, in which the valve is incorporated in the injection nozzle, and Fig. 3 shows a valve with a restrictor.

Fig. 1 shows a fuel injection device according to the invention, in which the valve is disposed between the injection line and the overflow-oil line. A diesel engine (not shown) drives an injection pump 1 which sucks fuel through a fuel supply pipe 2. The sucked fuel is pressurised and conveyed through an injection line 3 to an injection nozzle 4 of known construction and operation. The injection nozzle 4 has a high-pressure connection 5 connected to the injection line 3, and a low-pressure connection, more particularly an overflow-oil line connection 6, connected e.g. to a fuel tank or a delivery pump. A valve 7, more particularly a discharge valve, is disposed according to the invention near the injection nozzle 4 and connected between the high-pressure region 3.1 (formed by the injection line 3) and an overflow-oil line 8.

After fuel has been pressurised by the injection pump 1 and has travelled through the injection line 3 to the injection nozzle 4, the supplied fuel is injected through the nozzle 4 At the end of the injection process, the high-pressure volume in the injection line 3 is discharged through the valve 7 into the overflow-oil line 8. The pressure in the overflow-oil line 8 is kept sufficiently low to prevent bubbles of fuel vapour forming in the injection line 3. Since the valve 7 is disposed near the injection nozzle 4 and the fuel is discharged through the valve 7, the highpressure volume in the injection line 3 is reduced, so that fluctuations in the operating parameters of the engine, more particularly temperature fluctuations, do not influence the high-pressure volume, and consequently a defined amount of fuel will be available in the injection line 3 for the next injection process.

Fig. 2 shows a fuel injection device according to the invention in which the valve 7 is incorporated in the injection nozzle 4. The valve 7, connected between the high-pressure region 3.1 and the overflow-oil line 8, is disposed inside the casing of the injection nozzle 4, thus facilitating replacement or subsequent fitting of the injection nozzle 4 and valve 7. The operation of the fuel injection device described in Fig. 2 is similar to the fuel injection device described in Fig. 1.

Fig. 3 shows a valve 7 comprising a restrictor 9. To ensure a defined flow rate of fuel during discharge through valve 7, a restrictor 9, e.g. a constriction of the passage region, is provided in the passage region of valve 7 between the high-pressure region 3.1 and the overflow-oil line 8. Alternatively the bore of the passage region of valve 7 can be reduced or equivalent means can be used to reduce the discharge of fuel from the high-pressure region 3.1 to the pressure region of the overflow-oil line 8, in order to control the discharge rate.

The valve 7 equipped with the restrictor 9 is of use in an arrangement of the valve 7 according to Fig. 1 or according to Fig. 2.

8 - A fuel injection device C L A 1 1,1 S 1. A fuel iniection device comprising at least one injection pump (1) driven by a diesel engine and having its high-pressure connection (5) connected via an injection line (3) to an injection nozzle (4) which also has an overflowoil line connection (6), a valve (7) being provided in the high-pressure region, characterised in that the valve (7) is connected between the high-pressure region (3.1) and the overf low-oil line (8) and is disposed in the neighbourhood of the injection nozzle (4).

2. A fuel injection device according to claim 1, characterised in that the valve (7) is disposed between the injection line (5) and the overflow- oil line (8).

3. A fuel injection device according to claim 1, characterised in that the valve (7) is incorporated in the injection nozzle (4).

4. A fuel injection device according to any of the preceding claims, characterised in that the valve (7) is a discharge valve.

5. A fuel injection device according to any of the preceding claims, characterised in that the valve (7) has a restrictor (9).