GB2318388A

GB2318388A - Method of operating an electrically-actuated fuel-injection valve for i.c. engines

Info

Publication number: GB2318388A
Application number: GB9720628A
Authority: GB
Inventors: Winfried Moser; Stefan Kampmann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1996-10-15
Filing date: 1997-09-30
Publication date: 1998-04-22
Anticipated expiration: 2017-09-30
Also published as: GB9720628D0; GB2318388B; JPH10122084A; DE19642441A1

Abstract

The fuel-injection valve has a valve member 7 with a closing head 9 which protrudes out of the bore 7 and an electric adjusting member, eg a piezo stack 51, which can displace the valve member 7 outwards from the valve seat 13 against the force of a closing spring 35. The electric adjusting member 51 is controlled in such a manner that during an injection cycle it opens and then seals again the opening cross section between the valve seat 13 and the valve sealing surface 11 on a number of occasions in order to reduce pollutant emissions. A short injection pulse starting a time t 1 produces a pre-injection stroke h 1 followed, after a pause t 2 - t n , by several successive partial injections with full stroke h 2 .

Description

2318388 DESCRUMON METHOL) FOR THE PURPOSE OF ACTUATING A FUEL-INJECTION

VALVE FOR UfMRNAL COMBUSTION ENGINES The invention relates to a method for the purpose of actuating fuel- injection valves for internal combustion engines.

EP 0 218 895 discloses a fuel-injection valve for internal combustion engines, wherein a piston-shaped valve member is guided in an axial manner in a bore of a valve body which bore issues into the combustion chamber of the internal combustion engine. The valve member comprises on its combustion chamber side end a closing head which protrudes out of a bore of the valve body and whose end face, facing the valve body, forms a valve sealing surface. In order to control an injection opening croiss- section, this valve sealing surface on the valve member cooperates with a fixed valve seat surface which is formed on the combustion chamber side end face of the valve body and which surrounds the mouth of the bore. Furthermore, a fuel pressure duct formed between the bore and the valve member'issues at the valve seat which is connected to an injection line. When the injection valve is closed the valve member is held in position on the valve seat by a valve spring and is influenced directly by a piezo actuator for the purpose of performing the opening stroke which is directed outwards. In so doing, the opening stroke movement of the valve member is performed by supplying current to the piezo actuator which extends in an axial manner in the direction 2 of the valve member by means of hydraulic padding supported in a fixed manner on the housing and thus lifts the valve member.with its valve sealing surface from the valve seat so that the fuel can flow by way of the controlled opening cross section into the combustion chamber.

It is possible, in the case of the conical or screen jet produced, to achieve effective atomization even at low injection pressure owing to the larger jet surface, wherein the jet penetration depth can adjusted over the maximum opening stroke of the valve member.

However, the known injection method has the disadvantage that the injection valve, owing to two conflicting design criteria, can only be optimised with respect to a low level of NOx emissions or a low level of soot emissions, since a low level of NOx emissions requires the longest possible injection period and thus a small valve member stroke, whereas a low level of soot emissions requires a high jet penetration depth and thus the maximum possible valve member stroke.

However, the demands placed on modern internal combustion engines, in particular small diesel engines, require the lowest possible pollutant emissions both with respect to soot and NOx emission values.

In contrast to the aforegoing, in accordance with the present invention, there is provided a method for the purpose of actuating a fuelinjection valve for an internal combustion engine comprising a valve body having a bore which issues into the combustion chamber and in which a valve member is guided in an axially displaceable manner which valve member 3 comprises on its combustion chamber side end a closing head which protrudes out of the bore and on the end face of the said closing head, facing the valve body, is disposed a sealing surface which for the purpose of controlling an injection opening cross section cooperates with a valve seat surface, which defines a fuel pressure duct, on the combustion chamber side end face of the valve body, and further comprising an electric adjusting member which can displace the valve member outwards from the valve seat against the force of a closing spring, in which method the electric adjusting member is controlled in such a manner that during an injection cycle it opens and then seals the opening cross section between the valve seat and the valve sealing surface on a number of occasions.

A method in accordance with the invention has the advantage that the functions of injection period and jet penetration depth are decoupled from each other so that they can each be optimised individually and independently from each other.

This is achieved in an advantageous manner by virtue of a cyclic control of the electric adjusting member whereby the opening cross section at the injection valve is controlled in an intermittent manner during an injection cycle so that the injection quantity is injected into the combustion chamber in an controllable manner in partial quantities. Firstly, it is possible to inject a small pre-injection quantity which after a short injection pause is followed by the main injection quantity divided into several partial injection quantities, wherein in the case of a predetermined injection pressure the entire injection 4 quantity is dependent upon the number and the pulse duration of the individual partial injections. The injection period can be controlled independently of the maximum valve member opening stroke by way of the number and the pulse duration of the individual partial opening strokes so that noise and NOx emissions can be influenced in a direct manner. In particular, the injection pauses serve to produce an intensive mixture of exhaust gas and fresh air in the combustion chamber. By virtue of the localized "exhaust gas recirculation" on the one hand and the localized fall in temperature in the combusted mixture of fuel and air on the other hand it is possible to achieve a particularly low level of NOx emissions.

Since, in the partial load range of the internal combustion engine to be supplied, it is necessary for the jet penetration depth of the injection jet to be smaller with respect to the full load operation, the valve member stroke in the partial load range can be reduced with respect to the maximum stroke. Furthermore, it is advantageous to control the valve member stroke also in dependence upon charging pressure and final compression temperature, since the required jet penetration depth is also dependent upon these parameters of the internal combustion engine.

Moreover, the injection method in accordance with the invention renders it possible to shape the injection progression by way of the modulation of the valve member stroke of the individual partial opening pulses. In so doing, it is particularly advantageous, especially in the case of the first opening pulses, to perform an increasing valve member stroke in order to convey the fuel initially to the proximity of the pre-injected and already ignited quantity of fuel.

A rapidly switching solenoid valve or more suitably a piezo actuator is used as an electric adjusting member, wherein in this case the axial adjusting movement of the piezo actuator is enlarged with respect to the valve member by way of a hydraulic coupling element, which simultaneously serves to compensate length tolerances owing to the fluctuations in temperature and manufacturing tolerances on the piezo actuator.

In order to achieve a maximum frequency of the partial pulses on the valve member the piezo actuator can be exited in an advantageous manner at its natural frequency.

The piezo actuator is controlled by way of an electric control device which fixes the injection timing, injection quantity, pulse duration and injection pauses on the injection valve in a controlled manner according to performance characteristics in dependence upon operating parameters of the internal combustion engine to be supplied.

The fuel is supplied to the injection valve in a constant manner, for which purpose the pressure duct of the injection valve is connected by way of an injection line to a fuel collecting chamber (Common Rail) which is filled continuously with high pressure fuel by way of a high pressure fuel pump.

It is particularly advantageous to apply the injection method in accordance with the invention in the case of small direct injection diesel engines since these only require a small free jet length of the injection jet.

6 The invention is described further hereinafter by way of example only with reference to the accompanying drawings, in which:- Figure 1 is a sectional view of the fuel-injection valve and a schematic illustration of the connections, and Figure 2 is a diagram, in which the stroke of the piezo actuator and/or the valve member during an injection cycle is plotted over time.

The fuel-injection valve illustrated in Figure 1 comprises a cylindrical valve body 1, which protrudes with its one end face into a combustion chamber 3 of the internal combustion engine to be supplied. In the valve body 1 there is provided an axial stepped bore 5 which issues at the end face of the valve body 1 issuing into combustion chamber 3 and in which a piston shaped valve member 7 is guided in an axially displaceable manner. The valve member 7 comprises on its combustion chamber side end a closing head 9 which protrudes out of the bore 5 and whose annular end face, facing the valve body 1, forms a valve sealing surface 11. In order to control an injection opening cross section, this valve sealing surface 11 on the valve member cooperates with a valve seat surface 13 formed on the combustion chamber side end face of the valve body 1, wherein the valve sealing surface 11 and the valve seat surface 13 are formed in a conical manner. The valve seat surface 13 defines a pressure duct 15 in the valve body 1, which pressure duct is formed between the wall of the bore 5 and the valve member 7 and which on the other side is defined by virtue of an annular collar 17, which slides in the bore 5, on the valve member 7 and which pressure duct is 7 connected by way of a transverse bore 19 to an injection line 21 leading to a fuel collecting chamber 23. The fuel collecting chamber 23 (Common Rail), from which all injection lines lead off to the individual injection valves, is filled with high pressure fuel from a storage tank 29 by a high pressure fuel pump 25 by way of a delivery line 27.

For improved guidance the valve member 7 comprises on its end in the proximity of the combustion chamber a guide cross piece 31 which slides on the wall of the bore 5 and comprises through-going orifices for the fuel.

The valve member 7 protrudes, with its shaft part which is connected on the side remote from the combustion chamber to the annular collar 17, into a spring chamber 33 in the valve body 1, in which spring chamber is disposed a closing spring 35 which is supported in a fixed manner on a bore step 37 and influences the valve member 7 by way of a spring plate 39 in the closing direction towards the valve seat 13.

On the side remote from the closing spring 35 a shaft end 41 of the valve member 7 is connected to the spring plate 39 which with its free end face 43, remote from the combustion chamber, protrudes into a closed hydraulic working chamber 45 which is filled with a pressure medium, wherein the shaft end 41 is formed in two pieces with respect to the valve member 7 and is connected thereto at the spring plate 39.

The hydraulic working chamber 43 is defined at its end lying opposite to the end face 43 of the valve member 7 by the end face 47 of an 8 adjusting piston 49 which is connected at the other end to the end face of a piezo actuator 51 in the form of a cylindrical piezo stack. The end face 47 of the adjusting piston 49 of the piezo actuator 51 is larger than the end face 43 of the valve member shaft end 41 so that the, axial adjusting stroke movement of the piezo actuator 51 is converted by way of the hydraulic working chamber 45 into a larger adjusting stroke movement of the valve member 7.

The piezo actuator 51 is connected by way of an electric connection line 53 to an electric control device 55 which controls the supply of current to all piezo actuators 51 of the individual injection valves.

The fuel-injection valve for internal combustion engines functions in the following manner.

When the injection valve is in the closed state the piezo actuator 51 is currentless and its axial extension corresponds to the starting position. The closing spring 35 holds the valve member 7 with its valve sealing surface 11 in position on the valve seat 13, so that the injection opening cross section is sealed. The high pressure fuel of the collecting chamber 23 is located in the pressure duct 15 and progresses as far as the valve seat 13. The surfaces, which define the pressure duct 15 in an axial manner, on the closing head 9 and on the annular collar 17 are designed in such a manner that the valve member 7 is pressure compensated to an approximate extent so that it is not necessary for the closing spring 35 to overcome the high pressure fuel.

If an injection process is to take place at the injection valve the piezo actuator 51 is supplied with current by way of the control device 55 and 9 extends in an axial manner owing to this application of voltage. This axial extension of the piezo actuator 51 which is fixed in a stationary manner on its end remote from the combustion chamber causes the adjusting piston 49 to be displaced in the direction of the valve member 7 and this displacement is transmitted to the valve member 7 by way of the hydraulic working chamber 45 against the force of the closing spring 35, wherein owing to the conversion of the hydraulic coupling the opening stroke path is increased still further at the valve member 7. The valve member 7 lifts from the valve seat 13 and releases the opening cross section between the valve sealing surface 11 and the valve seat 13 by way of which the screen or conical jet required for the injection process passes into the combustion chamber 3 of the internal combustion engine.

In order achieve a combustion comprising the lowest possible level of pollutant emissions the injection procedure is divided into several partial injections during an injection cycle, as illustrated in the diagram of Figure 2.

The diagram of Figure 2 shows the opening stroke progression "h" of the valve member 7 over time "t" of an injection cycle.

At time tl a short injection pulse is executed initially with the opening stroke lil which triggers the commencement of the injection of a small pre-injection quantity which initiates the ignition in the combustion chamber 3. This short-time pulse results only in a partial opening stroke of the valve member 7 which is terminated at time 0, so that the valve member 7 returns again to the valve seat 13 and interrupts the injection procedure. After a short injection pause t2-tn the main injection is commenced at time tn and consists of several successive partial injections with a complete valve member stroke h2. The entire injection quantity is predetermined by way of the number and the pulse duration of the partial injections, wherein all parameters such as injection timing, injection quantity, pulse duration and injection pauses are adjusted in dependence upon performance characteristics.

The injection cycle is terminated by once again switching off the supply of current to the piezo actuator 51, so that the closing spring 35 moves the valve member 7 with its sealing surface 11 back to the valve seat 13 and the injection opening cross section is scaled.

Owing to the large number of interruptions in the injection procedure it is possible to decouple the functions of injection period and jet penetration depth from each other so that both functions can be tailored individually in an optimum manner to suit the requirements of the respective internal combustion engine.

Claims

11 CLAIMS

1. A method for the purpose of actuating a fuel-injection valve for an internal combustion engine comprising a valve body having a bore which issues into the combustion chamber and in which a valve member is guided in an axially displaceable manner which valve member comprises on its combustion chamber side end a closing head which protrudes out of the bore and on the end face of the said closing head, facing the valve body, is disposed a sealing surface which for the purpose of controlling an injection ope i g cross section cooperates with a valve seat surface, which defines a fuel pressure duct, on the combustion chamber side end face of the valve body, and further comprising an electric adjusting member which can displace the valve member outwards from the valve seat against the force of a closing spring, in which method the electric adjusting member is controlled in such a manner that during an injection cycle it opens and then seals the opening cross section between the valve seat and the valve sealing surface on a number of occasions.

2. A method according to claim 1, wherein, at the beginning of the injection cycle, an extremely short opening stroke pulse is first triggered by the adjusting member by virtue of which the opening cross section is opened for the purpose of releasing a small pre-injection quantity and that after a short injection pause the main injection takes place consisting of a plurality of partial injection quantities.

3. A method according to claim 2, wherein the injection 12 quantity and the injection progression can be controlled by way of the number and the pulse duration of the partial opening strokes.

4. A method according to claim 1, wherein in the case of a partial load of the internal combustion engine to be supplied, the opening stroke which is triggered by the electric adjusting member is reduced with respect to the maximum valve member opening stroke which is performed in the case of a full load.

5. A method according to claim 1, wherein the valve member opening stroke is controlled in dependence upon the charging pressure and the final compression temperature of the internal combustion engine to be supplied.

6. A method according to claim 1, wherein the injection timing, injection quantity, pulse duration and injection pauses are controlled in dependence upon performance characteristics.

7. A fuel-injection valve for the purpose of implementing the method according to claim 1, wherein the electric adjusting member is formed as a piezo actuator.

8. A fuel-injection valve according to claim 7, wherein the piezo actuator comprises a displaceable end face which defines a hydraulic working chamber which on the other side is defined by an end face, remote from the closing head, of the valve member, wherein the end face of the piezo actuator is larger than the end face of the valve member.

9. A fuel-injection valve according to claim 7, wherein the 13 piezo actuator is connected by way of an electric connection line to a control device.

10. A fuel-injection valve according to claim 7, wherein the fuel pressure duct which issues at the valve seat is connected in a continuous manner by way of an injection line to a fuel collecting chamber which is filled with high pressure fuel by means of a high pressure pump.

11. A method for the purpose of actuating the piezo actuator according to claim 7, wherein the piezo actuator is excited at its natural frequency during the injection cycle.

12. A method actuating a fuel-injection valve for an internal combustion engine, substantially as hereinbefore described with reference to the accompanying drawings.

13. A fuel-injection valve substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings