GB2110756A

GB2110756A - A fuel injection system for internal combustion engines

Info

Publication number: GB2110756A
Application number: GB08233725A
Authority: GB
Inventors: Frank Thoma; Christoph Burckhardt; Karlheinz Hoffmann
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1981-12-01
Filing date: 1982-11-26
Publication date: 1983-06-22
Also published as: FR2517369B1; GB2110756B; IT1148681B; FR2517369A1; IT8249589A0; DE3147467C1

Abstract

A high-pressure injection pump 2 delivers uncontrolled fuel quantities to an injection nozzle 5 via a connecting line 4 or, under the control of valves 8 and 11, to the fuel tank 7 via a return line 6. The valve 11 is provided in a bypass 9 around the valve 8 in which a precisely defined throttle 10 is located. Both valves 8, 11 are in the form of open or closed valves and are operated by electrical actuators 12, 13 which are actuated by an electronic control device 14 which responds to the operational conditions of the internal combustion engine. The quantity and timing of an initial injection is determined by closure of the valve 8 and that of a main injection by the period between closure of the valve 11 and reopening of the valve 8. <IMAGE>

Description

SPECIFICATION A fuel injection system for internal combustion engines The invention relates to a fuel injection system for internal combustion engines. One known system comprises a high-pressure injection pump which delivers unregulated quantities of fuel to an injection nozzle by way of a connecting line, and further comprises a return line for diverting fuel into a fuel tank, the return line including a control valve.

With an injection system of this type (East German Patent Specificationn 70213), a preinjection and a main injection can be effected by an arrangement of two injection lines having different lengths which lead from a closure member or pilot valve to an injection nozzle and of which the line intended for the pre-injection volume has a throttle station at a subsequent stage in the system.

With such a system, there is a fixed association between the pre-injection quantity and the main injection quantity.

German Offenlegungsschrift (Laid-open specification) No. 28 35 1 55 discloses the practice of varying the fuel supply for injection valves by means of a control valve, which is located in the fuel return line and which is actuated depending on operating parameters by an electric control circuit, so that fuel injection can be controlled in such a manner that the object of creating the desired fuel/air ratio is achieved. The problem underlying the present invention is to provide an injection system in which the beginning of injection, the end of injection, the quantity to be injected and the injection cycle or sequence can be precisely controlled. Moreover, control by electromagnetic switch means should also be possible.

According to the present invention there is provided a fuel injection system for internal combustion engines including a high-pressure injection pump, which is adapted to deliver unregulated quantities of fuel to an injection nozzle by way of a connection line, a return line for diverting fuel supplied by the injection pump into a fuel tan, the return line including a first pilot valve, a second pilot valve being, arranged together with a throttle of predetermined characteristics in a by-pass around the first pilot valve, both pilot valves being formed by one-way valves and both being adapted to be controlled, selectively, via respective electrical actuators, by an electronic control device responsive to the operational data of the internal combustion engine so that a pre-injection quantity of fuel is controlled by operation of the first one-way valve and a main injection quantity is controlled by operation of the second one-way valve.

In this way, injection can be satisfactorily controlled by an injection system having a simple high pressure injection pump without sloping edge control, without a controller and without an ignition timing gear.

By applying the measures according to the invention, an extremely precise metering of fuel can be achieved merely by connecting and disconnecting the pilot valves, which are in the form of one-way valves and which are provided in the return lines acting as fuel diverting lines, and as a result of the throttle having a fixed cross-section, with in particular the first one-way valve taking over three functions namely the beginning of injection at the optimum time in each case, the control of the quantity to be delivered and control of the end of injection, whilst the second one-way valve with the precisely defined downstream throttle takes over the function of the injection cycle.Thus, when the first one-way valve is closed, a partial quantity or pre-injection quantity is directed towards the injection nozzle and, upon closure of the second one-way valve, the full quantity is directed to the injection nozzle.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing, in which: Figure 1 shows a diagrammatically illustrated injection system, Figure 2 shows the controlled injection cycle, and Figure 3 shows the respective control positions of the valves which produce the injection cycle or sequence according to Fig. 2.

The injection system 1 shown in Fig. 1 consists of a high-pressure injection pump 2 having four pump elements 3 which are connected to respective injection nozzles 5, (only one of which is shown), by way of respective connecting lines 4.

Branching from each connecting line, at a short distance ahead, i.e. upstream, of the injection nozzle 5, is a return line 6 which is connected to a fuel tank 7. The return line 6 contains a pilot valve 8 which is in the form of a one-way valve and which either blocks or unblocks the flow of fuel through the line depending on whether it is closed or open.

The return line 6 has a by-pass 9 which passes around the one-way valve 8 and in which are arranged a throttle 10 having a fixed throttle cross-section and a pilot valve 11 which is also in the form of a one-way valve.

The two pilot valves 8 and 11 are adapted to be controlled by electrical actuators 12, 1 3 or relay valves which in turn can be actuated by an electronic control device 1 4 which records or collects the operational data of the internal combustion engine. Piezo control elements or actuators or magnet-controlled or piezo-controlled 'logistors' can be used as actuators.

The quantity to be injected is controlled from the beginning of injection, (which is adjustable), which is determined with the aid of a transducer 15, for example a magnetoresistor needle lift sensor, which is built into the injection nozzle 5. The transducer signal corresponding to the beginning of injection is transmitted to the electronic control device 14 whcih controls the injection cycle and the end of injection.

The high-pressure injection pump, which has neither a sloping edge control nor a controller, constantly delivers the initial quantity, i.e. the maximum quantity of fuel required by the engine, to each connecting line.

The injection nozzle 5 is closed since the required nozzle opening pressure is not attained when the one-way valves 8 and 11 are open. As soon as the electronic control device 14 actuates the relay of pilot valve 8 and the one-way valve 8 is thereby closed at the same time, firstly a part of the fuel flows away through the throttle 10 and the one-way valve 11 and a part of the fuel flows through the now open injection nozzle 5. Because at first only the one-way valve 8 is closed, a preinjection quantity is injected into the combustion chamber of the internal combustion engine (see injection cycle according to Fig. 2).

Only when the one-way valve 11 is closed is the main injection quantity injected by the nozzle 5. The end of injection is finally determined by opening the one-way valve 8.

Fig. 3 shows the positions of the two oneway valves 8 and 11 during an injection process, the continuous lines indicating the respective control position of the valve 8 and the broken lines indicating the respective control position of the second valve 11, the upper line of each indicating the period when the valve is closed and injection is taking place.

An injection system of this type, in which the functions are allotted to two pilot valves, enables precise and freely programmable control of the beginning of injection, the quantity to be injected and of the injection cycle. Since at least one of the pilot valves is opened between the injections, the undesirable subsequent or post-injection by the injection nozzle 5 is prevented by reflected pressure waves in the connecting line 4, thereby resulting in better engine combustion in terms of exhaust gas and noise emission.

Claims

1. A fuel injection system for internal combustion engines including a high-pressure injection pump, which is adapted to deliver unregulated quantities of fuel to an injection nozzle by way of a connection line, a return line for diverting fuel supplied by the injection pump into a fuel tank, the return line including a first pilot valve, a second pilot valve being arranged together with a throttle of predetermined characteristics in a by-pass around the first pilot valve, both pilot valves being formed by one way valves and both being adapted to be controlled, selectively, via respective electrical actuators, by an electronic control device responsive to the operational data of the internal combustion engine so that a pre-injection quantity of fuel is controlled by operation of the first one-way valve and a main injection quantity is controlled by operation of the second one-way valve.

2. A fuel injection system according to claim 1 wherein a transducer is operatively connected to the injection nozzle, which transducer supplies a signal indicative of the start of injection to said electronic control device.

3. A fuel injection system according to claim 2 wherein said transducer is a magnetoresistor needle lift sensor.

4. A fuel injection system according to claim 1, 2 or 3 wherein said throttle is disposed in said bypass upstream of said second pilot valve.

5. A fuel injection system for an internal combustion engine substantially as described herein with reference to and as illustrated in the accompanying drawings.