EP0741244B1 - Injection nozzle - Google Patents

Description

The invention relates to an injection nozzle for use in common rail systems according to the preamble of the main claim.

Such common rail injection systems for diesel engines are, for example, in the progress reports for the 15th Vienna Motor Symposium of the VDI Verlag, row 12 / no. 205 (1994), pages 36 to 53. Under the term "common rail" Systems summarized, the goal of which is on the one hand, the injection pressure from the engine speed and to make the injection quantity independent, and on the other hand the middle one Increase injection pressure. An essential feature of the Common Rail Systems (CR) lies in the decoupling of pressure generation and injection through a storage volume, which is the volume of one with the injectors of a multi-cylinder engine connected common high-pressure distribution line (common rail) and the Supply lines and the volumes available in the nozzle itself.

The injection process is in the prior art by an integrated in the injection nozzle Solenoid valve controlled. A direct control of the nozzle body or Nozzle needle has so far been able to use either a magnetic valve or piezoelectric or magnetostrictive actuators can be realized.

The return valve designed as a solenoid valve has due to its magnetic actuation two defined positions, a closed and a fully open position. So that the injection nozzle when the return valve is opened by means of the magnet does not open too quickly, a return throttle is provided downstream of the return valve. The timing is determined by suitable adjustment of the inlet throttle to the return throttle Characteristic of the injector set. A small cross section of the return throttle means a slow pressure drop across the working piston when opening the return valve and thus a good small quantity capability of the injection nozzle, what a pre-injection is advantageous. At the same time, a small return cross-section means one large minimum spray distance between two successive injections, because between the opening of the return valve and the pressure drop across the actuator piston a relatively long period of time passes. Systems with a small return throttle cross section are therefore suitable for a small quantity pre-injection and a widely offset one Main or post injection.

A large return throttle cross section pulls because of the rapid full opening of the injector a poorer ability to process small quantities results in a faster one Opening the nozzle body or the nozzle needle and thus enables shorter spraying intervals. A large return throttle diameter is therefore suitable for one or more Main injections.

From DE-A 20 28 442 is an injection nozzle according to the preamble of the main claim known. With this injector, the return valve is immediately piezoelectric operated by its valve member is arranged at the end of a ceramic column. The Ceramic column consists of a large number of cylinders stacked on top of each other and points Parting joints, in the helical and mutually connected Electrodes are embedded. The high voltage required to operate the ceramic column is generated in a jacket-shaped pulse transformer that surrounds the ceramic column. A rectangular pulse is applied to the primary side of the transformer to open the injection nozzle due to which the ceramic column contracts and the return valve opens. After the voltage pulse has ended, the ceramic column expands, so that the pilot valve closes. The operation is such that the return valve opens completely during a voltage pulse and outside of the voltage pulse closes completely so that the timing of the injection essentially through the cross section of the inlet throttle, the opening cross section of the return valve and the duration of the rectangular pulse is given. The resulting variability of the Injection course is relatively limited.

The invention has for its object an injection nozzle for use in common rail To create systems that both have a good small volume capability for a pre-injection also has a rapid main injection following the pre-injection or a clocked main injection.

This object is achieved with the features of the main claim. In that the valve member of the return valve can be opened analogously, can Return valve itself form a variable return throttle cross section, so that the injector is optimally adaptable to the respective requirements. Overall, with the injection nozzle according to the invention by appropriate control of the return valve a good small quantity capability for a perfect pre-injection as well carry out a main injection that follows quickly, possibly clocked. This results in a soft combustion with low soot values and low nitrogen oxide values achieved with good overall efficiency.

The actuating device according to claim 2 is advantageously a piezoelectric working institution. Because the actuator is not immediate the nozzle body, but operated the return valve, relatively small enough Lift out how they are achieved with piezo actuators.

The claim 3 characterizes an advantageous embodiment of the injector, which is particularly is precisely controllable.

A peculiarity of the embodiment according to claim 4 is that the valve member of the for example, a return valve designed as a flat valve in its closed position and so with the injector closed, constantly against the high, in the work area of Actuator piston effective system pressure must be kept in contact with the valve seat.

With the features of claim 5 it is achieved that the valve member by the the high system pressure acting in the work area even when in contact with the valve seat is maintained, which reduces energy consumption and operational reliability is enlarged. In the event of a fault in the actuating device, the valve member arrives thus when the system pressure builds up in increasingly fixed contact with the seat, which means that Injector remains reliably closed and no fuel is sprayed.

Claims 6 and 7 characterize advantageous embodiments of the valve according to Claim 5.

Claims 8 and 9 are based on two advantageous methods using one according to the invention Injector directed. It does with the features of the claim 8 achieved that the main injection can follow the pilot injection for a short time. With the features of claim 9 it is achieved that the injection nozzle is extraordinary closes quickly, which is beneficial for combustion.

The invention is described below with reference to schematic drawings, for example and explained with further details.

Fig. 1

ein Gesamtschema eines Common-Rail Systems,

Fig. 2

das Hydraulikschema einer erfindungsgemäßen Einspritzdüse,

Fig. 3

einen Schnitt durch den vorderen Abschnitt einer erfindungsgemäßen Einspritzdüse,

Fig. 4

Hub-, Druck- und Durchsatzverläufe einer Einspritzung unter Verwendung einer erfindungsgemäßen Einspritzdüse,

Fig. 5

Hubverläufe zweier Steuerverfahren,

Fig. 6

das Hydraulikschema einer abgeänderten Ausführungsform einer erfindungsgemäßen Einspritzdüse,

Fig. 7

ein Schema des Rücklaufventils gemäß Fig. 6 und

Fig. 8

einen Schnitt durch den vorderen Abschnitt der Einspritzdüse gemäß Fig. 6.

They represent:

Fig. 1

an overall diagram of a common rail system,

Fig. 2

the hydraulic diagram of an injection nozzle according to the invention,

Fig. 3

3 shows a section through the front section of an injection nozzle according to the invention,

Fig. 4

Stroke, pressure and throughput curves of an injection using an injection nozzle according to the invention,

Fig. 5

Stroke curves of two control methods,

Fig. 6

the hydraulic diagram of a modified embodiment of an injection nozzle according to the invention,

Fig. 7

a scheme of the return valve according to FIG. 6 and

Fig. 8

6 shows a section through the front section of the injection nozzle according to FIG. 6.

1 is a fuel tank 2 via a filter and a prefeed pump 4 with a Common rail (CR) high pressure pump 6 connected. Leading from the CR high pressure pump a line to a distribution line (common rail) 8, which via lines 10 with the Injection nozzles assigned to each cylinder of a multi-cylinder internal combustion engine 12 is connected.

The injection nozzles 12 are via return lines 14 with one leading to the tank 2 Return line 16 connected.

The system pressure is limited by means of a limiting valve 18 and can last up to 2000 bar.

An electronic control unit 20 is with its outputs with the high pressure pump 6 and connected to the injectors 12. The inputs 22 of the control unit are with a Pressure sensor 24 of the distributor line 8 and other sensors, not shown, for example for the position of an accelerator pedal, driving speed, temperatures, Boost pressure, air mass, speed, etc.

Fig. 2 shows the basic structure of an injection nozzle with the associated hydraulic diagram.

The injection nozzle 12 contains a nozzle body 26 which ends in a nozzle needle, which is in contact with a valve seat when the injector is closed. The nozzle body 26 extends through a nozzle space 28 which is connected to the feed line 10.

The nozzle body 26 is connected to an actuator piston 30 or is formed in one piece, which works in a working space 32, which via an inlet throttle 34 with the supply line 10 is connected. The working space 32 is further connected to the via a return valve 36 Return line 14 connected.

To actuate the return valve 36, its valve member 38 is provided with a piezo actuator 40 trained actuator connected to the 42 through their connections Control unit 20 is connected.

Such piezo actuators are known per se and are constructed like capacitors whose Dielectric made of piezoelectric material, for example lead zirconate titanate ceramic consists. Modern actuators work with field strengths of up to 2000 V / mm and reach relative changes in length of up to 1.5 ‰. In the example shown you can use a length of the piezo actuator 40 of approximately 100 mm thus a defined stroke of over Achieve 0.1mm, what an analog change in the opening cross-section of the return valve 36 completely depending on the voltage at the terminals 42 is sufficient.

Alternatively, the piezo actuator 40 could also be a magnetostrictive actuator in which magnetostrictive material is arranged within a current-carrying coil.

Fig. 3 shows a section through an executed example of an injection nozzle, wherein the Construction of the nozzle needle and its interaction with the seat known per se is, for example as in the automotive paperback, Bosch, VDI Verlag 1991, on page 509.

It is essential that the effective area with which the actuator piston 30 is in the work area 32 is applied, is larger than the effective area with which the nozzle body 26 in Nozzle chamber 28 or the nozzle needle is acted upon upstream of the valve seat, so that at the same pressure in the work chamber 32 and nozzle chamber 28, the nozzle body 26 in Closed position is pushed.

The function of the arrangement described is as follows:

When the return valve 36 is closed, it arises in the working space 32 and the nozzle space 28 the pressure prevailing in the feed line, which causes the nozzle body 26 in the closed position urges. If the valve member 38 is opened by applying voltage to the piezo actuator 40, the pressure escapes from the working space 32 if the opening is sufficiently wide Return valve 36 can flow through the inlet throttle 34 faster than fuel, so that when the pressure in the working space 32 decreases, the nozzle as a result of the pressure in Nozzle chamber 28 opens. If the return valve 36 is closed, the high Pressure in the working space 32 again, so that the injector closes.

The entire pressure level in the feed line 10 can, depending on the operating conditions Pressure sensor 24 detects and, by the control unit 20 by controlling the high pressure pump 6 controlled, changed.

Kurve I

den Hub hv des Ventilgliedes 38 (proportional zur Spannung an den Anschlüssen 20), wobei der kleinere Hub 0,03mm und der größere Hub 0,06mm beträgt,

Kurve II

den Hub hn des Düsenkörpers 26 bzw. der Düsennadel,

Kurve III

den Druck pi im Düsenraum 28,

Kurve IV

den Druck pa im Arbeitsraum 32,

Kurve V

die Spritzrate SR, das heißt den aus der Einspritzdüse austretenden Volumenstrom an Kraftstoff und

Kurve VI

die integrierte Spritzmenge Qe.

4 shows measurement protocols of a control method, wherein:

Curve I

the stroke hv of the valve member 38 (proportional to the voltage at the connections 20), the smaller stroke being 0.03 mm and the larger stroke 0.06 mm,

Curve II

the stroke hn of the nozzle body 26 or the nozzle needle,

Curve III

the pressure pi in the nozzle chamber 28,

Curve IV

the pressure pa in the work area 32,

Curve V

the spray rate SR, that is to say the volume flow of fuel emerging from the injection nozzle and

Curve VI

the integrated spray quantity Qe.

In the example shown, the diameter of the inlet throttle 34 was 0.30 mm and the Bore diameter of the return valve 36 (Fig. 3) 0.7mm.

As can clearly be seen from curves I and II, the opening of the injection nozzle or the stroke movement of the nozzle body 36 the small stroke of the valve member 38 of the return valve 36 with a large delay, so that a soft pre-injection begins is. The end of the pre-injection immediately follows the end of the voltage application of the piezo actuator 40 or the closing of the return valve 36 an excellent small volume capability given by the small stroke of the Valve member 38, the return valve 36 acts as a small return throttle. Will that Return valve 36 now further by applying more voltage to the actuator 40 opened, the injector opens with less delay than the opening of the return valve now acting as a throttle with a considerably larger cross section 36. The closing of the injection valve and thus the end of the main injection follows the closing of the return valve 36, however, now with a greater delay since in the working space 32 the full pressure has to build up again by the fuel Inlet throttle flows through 34.

5, curves Ia and IIa correspond to curves I and II of FIG. 4. As can be seen the main injection takes place here clocked by controlling the return valve 36 in this way is that the nozzle body 26 always as soon as it almost reaches its full stroke has, closes again.

Curves Ib, IIb and Ic, IIc show a comparison of a stroke of a main injection, in which the return valve 36 is opened once with a constant amplitude (Ib) and the other time the opening amplitude of the return valve 36 to a reduced value is set as soon as the opening of the injection nozzle has started or the Nozzle body 26 has lifted substantially from its seat. As can be seen, the control system leads of the return valve 36 according to FIG. 1c for a faster closing of the injection nozzle Closing the return valve 36, which is advantageous with regard to the burning process.

FIG. 6 shows the hydraulic diagram of an embodiment somewhat modified compared to FIG. 2 an injection nozzle, the same reference numerals for functionally identical parts be used. The main difference to Fig. 2 is that in the former Example the valve member 38 on the downstream side of the seat of the return valve 36 is arranged and thus to close the valve against the high System pressure must be constantly pushed into the closed position, whereas in the embodiment 6, the valve member 38 in the flow direction in front of the valve seat is arranged.

FIG. 7 shows the valve diagram of the return valve 36 according to FIG. 6.

A valve chamber 44 has a connection opening for connecting the connecting line 35 and a return opening 46 through which the valve chamber 44 into a space 48 passes, which is connected to the return line 14. The return opening is like this formed that its edge has a valve seat 50 for the valve member formed as a ball 38 forms. The ball 38 is pressed against the valve seat 50 by a spring 54. For Actuation of the ball 38 protrudes through the space 48 and the return opening 46 with the piezo actuator 40 connected actuator 56, which, as shown in Fig. 4, in the space 48 downstream of the branch of the return line 14 with sealing is led.

Fig. 8 shows a section through an executed example of an injection nozzle, wherein the Construction of the nozzle needle and its interaction with the seat known per se is, for example as in the automotive paperback, Bosch, VDI Verlag 1991, on page 509.

A housing sleeve 60 ending in the injection nozzle 12 is provided with a further housing part 62 screwed. In a bore in the housing part 62, in which the feed line 10 is formed, the piezo actuator 40 is received with the actuator 56, the is sealed against the piezo actuator 40 by means of a seal 64 and by means of a Flange works against a spring 66.

The housing sleeve 60 and the housing part 62 span two further housing bodies between them 68 and 70. The actuator piston 30 works in the housing body 68. By doing The inlet throttle 34 is formed in the housing body 70. The housing body 70 furthermore has a multi-graded through hole on the connecting line 35, the Valve chamber 44, the return opening 46 (Fig. 7) with the valve seat 50 and the space 48 (Fig. 7) from which the return line 14 branches off. The actuator 56 extends through the space formed in the upper end of the through hole of the housing body 70 48 with a smaller diameter or with grooves on its outer surface provided approach 72 which actuates the ball 38 through the return opening. The Return line 14 branches off from an annular space through an enlarged bore step 8 is formed at the upper end of the through bore of the housing body 70 according to FIG.

The function of the described arrangement is as follows:

In the de-energized state of the piezo actuator 40, the actuator 56 protrudes so far into the Return opening 46 that it with the spring 54 in contact with the valve seat 50th crowded ball 52 is not engaged. If the system pressure in the supply line 10 builds up, the ball 52 is also in contact with the valve seat by the system pressure 50 urged so that the return valve 36 is reliably closed and thus that entire injector is closed reliably.

When the piezo actuator 40 is energized or electrically actuated, the Ball 52 by means of the actuator 56 against the system pressure and the spring force from Valve seat 50 is lifted, whereupon the pressure in the working space drops and that Fuel injector injected. This spraying process, as in the main application (DE 195 16 245.5) described in detail, can be precisely controlled. To the seal 64 (Fig. 4), the Guide of the actuator 56 seals against the space 48 are not high Requirements because this seal is not in any condition with the high system pressure is applied.

It is understood that the method described with reference to FIGS. 4 and 5 with the embodiment 6 can be carried out particularly advantageously.

Claims (9)

1. An injection nozzle for use in common-rail systems with a nozzle body (26) fitted with an actuator piston (30) and which, when the injector nozzle is in the closed state, bears on a seat and, upstream of the seat, defines a nozzle space (28) which is connected to the high pressure line of the common-rail system, and with a working space (32) for the actuator piston (30) and which is connected to the high pressure line via a feed throttle (34), whereby the effective surface area of the actuator piston (30) is greater than the effective surface area of the nozzle body in the nozzle chamber, and with a return line (14) leading from the working space and through a return orifice of a return valve (36) and with an actuating means operated by an electrical signal to actuate the valve member of the return valve, characterised in that the actuating means is a device (40) which, in the same way as the electrical signal, adjusts the valve member (38) of the return valve (36) so that the return valve forms for the return line (14) a throttle the cross-section of which can be varied at will between two extreme positions.
2. An injection nozzle according to claim 1, characterised in that the actuating means is a piezoelectrically operating device (40).
3. An injection nozzle according to claim 1 or 2, characterised in that the effective cross-section of the opening of the return valve (36) alters at least at the start of the valve being opened and approximately in proportion to the stroke ofthe valve member (38).
4. An injection nozzle according to one of claims 1 to 3, characterised in that the valve member (38) of the return valve (36) is disposed on that side of a return valve aperture which can be occluded by the valve member and which is towards the return line (14).
5. An injection nozzle according to one of claims 1 to 3, characterised in that the valve member (38) is disposed in a valve chamber (44) of the return valve (36), said valve chamber (44) being connected by a connecting line (35) to the working space (32) and to the return line (14) through a return orifice (46), and in that, actuated by the device (40), an actuating member (56) for the valve member (38) passes through the return orifice (46) and in that a valve seat (50) co-operating with the valve member (38) is so constructed that when it bears on the valve seat the valve member closes the connection between the valve chamber (44) and the return line (14).
6. An injection nozzle according to claim 5, characterised in that in the inoperative state of a piezo actuator (40) of the actuating device, the valve member (38) bears on the valve seat (50).
7. An injection nozzle according to claim 5 or 6, characterised in that the valve member (38) is constructed as a sphere.
8. A method of controlling a multi-phase injection of a directly injected diesel engine, employing an injection nozzle according to one of claims 1 to 7, characterised in that the electrical signal for the actuating device (40) of the return valve (36) is maintained at a low value for free injection and at a higher value for subsequent main injection with a greater injection quantity after shut-down in order to close the injection nozzle.
9. A method of controlling a multi-phase injection of a directly injected diesel engine, employing an injection nozzle according to one of claims 1 to 7, characterised in that the electrical signal for the actuating device (40) of the return valve (36) is maintained at a high value for a first period of time, for opening the injection nozzle and then, when the injection nozzle is opened, is maintained at a high value and then, with the injection nozzle open, is maintained at a lower value to prepare for a rapid closure of the injection nozzle.

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