Injection nozzle

The present invention relates to an injection nozzle (1) for an internal combustion engine, in particular in a motor vehicle. A first nozzle needle (3) controls at least one first injection opening (5). A second nozzle needle (4) controls at least one second injection opening (6). A control chamber (32) is connected via a throttle line (35) to a pressure chamber (34) in which it is possible to adjust the injection pressure. A first control piston (41) cooperates with a first needle unit (17) that includes the first nozzle needle (3) and the first control surface (43) of this first control piston (41) can be acted on by the control pressure prevailing in the control chamber (32). In the closed position of the first nozzle needle (3), there is an axial play (44) between the first control piston (41) and the first needle unit (17). A second control piston (42) cooperates with a second needle unit (30) that includes the second nozzle needle (4) and can be acted on with the control pressure on a second control surface (45). In a closed position of the second nozzle needle (4), the second control piston (42) rests against the second nozzle needle (4) on the second needle unit (30). At middle to high pressures in the pressure chamber (34), both nozzle needles (3, 4) can close quickly. With a rapid pressure increase in the pressure chamber (34), the second nozzle needle (4) can open quickly and the two nozzle needles (3, 4) can close quickly. With a relatively low to middle speed pressure increase in the pressure chamber (34), the second nozzle needle (4) does not open or only opens at a higher pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 2004/001978 filed on Sep. 7, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improved fuel injection nozzle for an internal combustion engine, in particular in a motor vehicle.

2. Description of the Prior Art

An injection nozzle of the type with which this invention is concerned is known, for example, from DE 100 58 153 A1 and has a first nozzle needle embodied in the form of a hollow needle and a second nozzle needle situated coaxial to the first nozzle needle. The first nozzle needle can control an injection of fuel through at least one first injection opening while the second nozzle needle can control the injection of fuel through at least one second injection opening. A control piston is provided for actuating the second nozzle needle and axially cooperates with the second nozzle needle or a second needle unit that includes the second nozzle needle. A control surface of this control piston oriented away from the injection openings is situated in a control chamber and can be acted by the control pressure prevailing therein. In a closed position of the second nozzle needle, the control piston rests axially against the second nozzle needle or second needle unit.

The first nozzle needle in the known injection nozzle can be directly controlled with the injection pressure, i.e. the first nozzle needle opens as soon as a sufficiently high injection pressure acts on a corresponding pressure shoulder of the first nozzle needle. If a fuel injection is to be executed only by means of the at least one first injection opening, then the control chamber is subjected to a correspondingly high control pressure so that the second nozzle needle remains closed. If a fuel injection is to also be executed by means of the at least one second injection opening, then the pressure in the control chamber is reduced until the injection pressure acting on a corresponding pressure shoulder on the second nozzle needle causes the second nozzle needle to open. The second nozzle needle is consequently controlled not by means of the injection pressure, but by means of the control pressure prevailing in the control chamber, which is also referred to as servo control. It is relatively expensive to implement a servo control this kind.

SUMMARY AND ADVANTAGES OF THE INVENTION

The injection nozzle according to the present invention has the advantage over the prior art that both the first nozzle needle and the second nozzle needle are controlled directly as a function of the injection pressure. The injection nozzle according to the present invention thus eliminates the costs of implementing a servo control. Moreover, the injection nozzle according to present invention has comparatively high closing dynamics for both nozzle needles and also has high opening dynamics for the second nozzle needle at comparatively high injection pressures. As a result, the nozzle needles react very quickly to the closing so that extremely short closing times can be achieved. The second nozzle needle then also reacts to the opening with a corresponding rapidity so that relatively short opening times for the second nozzle needle can also be achieved.

Thanks to the proposed throttled coupling of the control chamber to the pressure chamber, a pressure compensation between the pressure chamber and the control chamber only occurs in a delayed fashion. In order to open the nozzle needles, the pressure in the pressure chamber, namely the injection pressure, is increased in order to act directly on a corresponding pressure shoulder of the first nozzle needle. With sufficient injection pressure, the first nozzle needle opens. When the first nozzle needle is opened, the injection pressure can also build up against a corresponding pressure shoulder of the second nozzle needle. Since the pressure in the control chamber rises significantly more slowly, the second nozzle needle is thus already able to open at low injection pressures, i.e. earlier. In the closing of the nozzle needles, the delayed pressure compensation between the control chamber and the pressure chamber results in a shortening of the closing times. In order to close the nozzle needles, the injection pressure in the pressure chamber is reduced. This reduces the pressure acting on the pressure shoulders of the nozzle needles in the opening direction. The pressure in the control chamber cannot fall as quickly, thus resulting in very powerful closing forces for the nozzle needles, which forces accelerate, i.e. shorten, the closing process of the two nozzle needles. The essential thing here is that an additional servo valve is not required for triggering the second nozzle needle to open and close.

According to an advantageous embodiment form, a first closing spring can be provided, which, on the one hand, drives the first nozzle needle or first needle unit in the closing direction and on the other hand, directly or indirectly drives the first control piston into an initial position in which there is an axial play between the first control piston and the first nozzle needle or first needle unit. Because of this design, there is an axial play between the first control piston and the first nozzle needle or first needle unit when the first nozzle needle is in its closed position. When the first nozzle needle opens, it can lift independently of the first control piston within the range of the axial play, as a result of which the first nozzle needle is decoupled from the forces acting on the first control piston in the control chamber.

According to a preferred modification, the first control piston can constitute a first stroke stop for the first nozzle needle or first needle unit in such a way that in an open position of the first nozzle needle, the first control piston comes into direct axial contact with this first nozzle needle or the first needle unit. For the closing process, this means that the first control piston can transmit the compressive force prevailing in the control chamber directly to the first nozzle needle or first needle unit, in particular without an idle stroke. On the one hand, this achieves a rapid reaction of the first nozzle needle and on the other hand, makes it possible to avoid generating noise.

In another advantageous modification, the first control piston can constitute a second stroke stop for the second nozzle needle or second needle unit in such a way that in an open position of the second nozzle needle, the first control piston comes into axial contact directly against this second nozzle needle or second needle unit. On the one hand, this embodiment form also lends the first control piston a double function and on the other hand, it assures a rapid reaction of the second nozzle needle during closing; here, too, it is possible to avoid an idle stroke and a consequent generation of noise.

Other important characteristics and advantages of the injection nozzle according to the present invention are disclosed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According toFIG. 1, an injection nozzle1according to the present invention has a nozzle body2in which a first nozzle needle3and a second nozzle needle4are contained so that they can execute a stroke motion. The nozzle body2contains at least one first injection opening5and at least one second injection opening6. Usually, several first injection openings5and/or several second injection openings6are provided, which are distributed symmetrically, in particular with reference to a longitudinal axis7of the nozzle body2or nozzle needles3,4, for example in a star pattern. Via the injection openings5,6, fuel can be injected or dispensed into an injection chamber8, which can be constituted, for example, by a combustion chamber of a cylinder associated with the injection nozzle1or by a mixture-forming chamber leading to the respective cylinder.

A first needle guide9supports the first nozzle needle3so that it can execute a stroke motion in the nozzle body2and control the at least one first injection opening5. To this end, the first nozzle needle3cooperates with a first sealing seat10, which, in terms of a supply of fuel to the injection openings5,6, is situated upstream of the at least one first injection opening5. The fuel supply includes a fuel supply line11that extends inside the nozzle body2and leads to a nozzle chamber12. The nozzle chamber12extends via an annular chamber13to the injection openings5,6. In the nozzle chamber12and/or the annular chamber13, the first nozzle needle13has at least one first pressure shoulder14, which is designed so that a first seat cross-sectional area15of the first sealing seat10is smaller than a first guide cross-sectional area16of the first needle guide9.

Furthermore, the first nozzle needle3here is a component of a first needle unit17, which, as an example here, includes a coupling sleeve18and an intermediate element19situated between the coupling sleeve18and the first nozzle needle3. The components of the first needle unit17, i.e. in this case the first nozzle needle3, the intermediate element19, and the coupling sleeve18, constitute a unit that can execute a shared stroke motion and is designed to transmit compressive forces. It is fundamentally possible for the individual components of the first needle unit17to be comprised of separate elements that merely rest against each other at their axial end surfaces without being directly fastened to one another. It is also fundamentally possible to fasten at least two of the individual components to each other or to combine them into an integrated component.

The first nozzle needle3or first needle unit17cooperates with a first closing spring20that prestresses the first nozzle needle3in a closing direction21symbolized by an arrow. In the embodiment form shown here, the first closing spring20rests against the intermediate element19at one end and at the other end, rests against a drive ring22, which in turn rests by means of a stop sleeve23against the nozzle body2, which for this purpose, has a correspondingly formed shoulder24, protruding radially inward in this case, that acts as a stop. In an alternative design, the stop sleeve23can also be attached to the nozzle body2or formed onto it in an integral fashion.

In addition, the first nozzle needle3is embodied in the form of a hollow needle so that the second nozzle needle4can be situated coaxially inside the first nozzle needle3. The second nozzle needle4is supported so that it can execute a stroke motion in a second needle guide25inside the first nozzle needle3. The second nozzle needle4cooperates with a second sealing seat26, which is situated, in terms of the fuel supply, downstream of the at least one first injection opening5, but upstream of the at least one second injection opening6. Correspondingly, the second nozzle needle4serves to control the at least one second injection opening6. At its end oriented toward the injection openings5,6, the second nozzle needle4is provided with at least one second pressure shoulder27that is embodied so that a second seat cross-sectional area28of the second sealing seat26is smaller than a second guide cross-sectional area29of the second needle guide25.

The second nozzle needle4is a component of a second needle unit30, which, in addition to the first nozzle needle3, includes at least one coupling rod31. The coupling rod31extends inside the first nozzle needle3and inside the coupling sleeve18. In addition, the intermediate element19is embodied in the form of an annular body with an opening in the center so that the coupling rod31can also extend coaxially through the intermediate element19. The second needle unit30, too, can be loaded with pressure and execute a stroke motion as a whole.

The injection nozzle1according to the present invention is also equipped with a control chamber32that communicates with a pressure chamber34via a throttle line33. The throttle line33has a predetermined flow resistance, which can be suitably embodied in the form of a corresponding throttle35. The pressure chamber34cooperates with a pressure generating device or fuel delivery unit, whose pressure generating action is schematically represented here in the form of a piston36that can execute a stroke motion. By means of the stroke motion of piston36, the pressure in pressure chamber34can be controlled. However, in actual practice, the pressure generating device or fuel delivery unit might ultimately be, for example, a high-pressure fuel pump that supplies the injection nozzle1with the required high fuel pressure. The injection nozzle1shown here suitably constitutes a component of a so-called “unit injector”. In an internal combustion engine that operates with a unit injector system for fuel injection, each cylinder is associated with its own unit injector.

The pressure chamber34communicates with the fuel supply line11via a connection37; the connection37is attached to the fuel supply line11between the injection openings5,6and a valve38. The valve38, in particular a solenoid valve, serves to open and close the fuel supply line11. When the valve38is open, the fuel flows from the pressure chamber34through the connection37into the fuel supply line11and from there, in accordance with an arrow39, away from the injection openings5,6, and for example into a reservoir suitably constituted by the fuel tank of the internal combustion engine. Since the reservoir is comparatively unpressurized, it is not possible for high pressure to build up in the fuel supply line11. When the valve38is closed, the fuel cannot escape into the reservoir and therefore flows in accordance with an arrow40toward the injection openings5,6, thus simultaneously generating the required high pressure.

The injection nozzle1according to present invention is also equipped with a first control piston41and a second control piston42. The first control piston41is embodied in the form of a hollow piston. The second control piston42is situated coaxially inside the first control piston41.

The first control piston41cooperates with the first nozzle needle3or first needle unit17.

To this end, in the starting position depicted here, which occurs when the first nozzle needle3is closed, the first control piston41rests against the drive ring22so that the drive ring22and the first closing spring20support it against the intermediate element19and consequently against the first needle unit17. At an end oriented away from the injection openings5,6, the first control piston41also has a first control surface43, which is situated in the control chamber32so that the control pressure prevailing in the control chamber32acts on the first control surface43of the first control piston41in the closing direction21. Furthermore, the first control piston41is dimensioned and positioned so that in the initial position of the first control piston41depicted here, there is an axial play44between the first control piston41and the first nozzle needle3or first needle unit17. In the embodiment form depicted here, the axial play44is embodied in the form of an axial distance between the axial ends of the first control piston41and the coupling sleeve18that are oriented toward each other.

By contrast, the second control piston42rests permanently against the second nozzle needle4or, as in this case, against the second needle unit30, i.e. the second control piston42rests against the end of the coupling rod31oriented toward it. The second control piston42thus comprises a component of the second needle unit30, whose components cooperate with one another to transmit pressure. It is also possible for at least two of the components of the second needle unit30to be attached to each other or for these components to comprise an integrally joined unit.

The second control piston42extends through the first control piston41and likewise protrudes into the control chamber32. At an end oriented away from the injection openings5,6, the second control piston42has a second control surface45so that the control pressure prevailing in the control chamber32can also act on the second control surface45of the second control piston42. The control pressure is not exerted directly on the control piston42but rather indirectly by means of a spring plate46, which is supported so that it can execute a stroke motion in the control chamber32. In the embodiment form depicted here, the spring plate46occupies the entire cross section of the control chamber32but has at least one pressure compensation opening47that connects the two separate axial sides48and49of the spring plate46so that they can communicate with each other, i.e. the at least one pressure compensation opening47allows a part of the control chamber32oriented toward the one axial side48to communicate with a part of the control chamber32oriented toward the other axial side49. As a result, the same control pressure prevails in both parts of the control chamber32separated from each other by the spring plate46. The pressure compensation openings47are dimensioned so that even with dynamic pressure changes in the control chamber32, these pressure changes occur in the two parts of the control chamber32at essentially the same time. Consequently, on the two axial sides48and49of the spring plate46, the same control pressure prevails as the one exerted on the second control surface45of the second control piston42in the control chamber32by means of the spring plate46since the second control surface45of the second control piston42rests against the spring plate46. Alternatively, the at least one pressure compensation opening47can also be designed so that the opening and closing speed of the second needle unit30achieve a desired optimal speed.

The second nozzle needle4or second needle unit30is associated with a second closing spring50, which, in the embodiment form depicted here, is situated in the control chamber32and rests against the spring plate46at one end and rests against the wall51of the nozzle body2at the other, which wall51axially delimits the control chamber32at an end oriented away from the injection openings5,6.

The injection nozzle1according to present invention functions as follows:

In the initial state depicted here, both of the nozzle needles3,4are closed so that no fuel injection is taking place. The valve38is open so that a fuel volume possibly supplied into the pressure chamber34can escape into the reservoir in accordance with the arrow39.

For certain operating states of the internal combustion engine, it can be necessary for a fuel injection to occur exclusively by means of the at least one first injection opening5. In order to implement a fuel injection exclusively by means of the at least one first injection opening5, the valve38is closed and as a result, the pressure in the pressure chamber34increases to a relatively low elevated injection pressure. The pressure increase in the pressure chamber34spreads via the fuel supply line11into the nozzle chamber12and into the annular chamber13so that it also acts against the at least one first pressure shoulder14of the first nozzle needle3. The forces engaging the at least one first pressure shoulder14act in an opening direction52symbolized by an arrow and consequently counter to the closing force of the first closing spring20. With a sufficient elevated injection pressure, the force equilibrium acting on the first nozzle needle3or first needle unit17reverses, yielding a resulting force acting in the opening direction52. It is then possible for the first nozzle needle3to lift away from the first sealing seat10. As a result, the at least one first injection opening5communicates with the annular chamber13so that fuel can be dispensed into the combustion chamber8through the at least one first injection opening5.

As soon as the first nozzle needle3opens, it is possible for a pressure acting in the opening direction to build up against the at least one second pressure shoulder27of the second nozzle needle4. With the relatively low elevated injection pressure that is set in this instance, though, the second nozzle needle4remains closed since the forces acting in the closing direction21, i.e. the closing force of the second closing spring50and the force of the control pressure against the second control surface45still predominate.

With the relatively low elevated injection pressure, the delayed pressure buildup in the control chamber32has either no effect or hardly any effect on the opening behavior of the first nozzle needle3. The control pressure prevailing in the control chamber32is consequently great enough to transmit sufficient closing forces to the second needle unit30by means of the second control piston42so that the second nozzle needle4remains closed. In addition, due to the axial play44, the first nozzle needle3or first needle unit17is decoupled from the first control piston41as long as the closing force acting on the first control surface43is not greater than the closing force exerted by the first closing spring20. In any case, as long as this condition exists, the first control piston41cannot move the drive ring22in the closing direction21when a pressure increase occurs in the control chamber32.

The opening movement of the first nozzle needle3or first needle unit17can be limited by means of a first stroke stop53, which is embodied by way of example here axially between the first control piston41and the coupling sleeve18, i.e. at the end of its opening stroke, the first needle unit17comes into contact with the first control piston41.

Alternatively, the first stroke stop53′ can also be embodied, for example, between the first nozzle needle3and a corresponding shoulder54of the nozzle body2. In this embodiment form, then, in the closed position of the first nozzle needle3, the axial play44is greater than an axial distance between the above-mentioned shoulder54of the nozzle body2and the axial end surface of the first nozzle needle3that cooperates with it.

In order to close the first nozzle needle3, the valve38is opened so that the relatively low elevated injection pressure in the fuel supply line11is completely discharged. Consequently, the closing forces in the first nozzle needle unit17predominate once again, driving the needle unit17in the closing direction21. As soon as the first nozzle needle3has moved into its first seat10, the injection process is terminated. The delayed pressure decrease in the control chamber32here does not assist the closing motion of the first needle unit17since the closing force of the first closing spring20is sufficient to hold the first control piston41in its initial position.

In other operating states of the internal combustion engine, it can be necessary to dispense more fuel at a mid-level elevated injection pressure exclusively by means of the at least one first injection opening5. To this end, the valve38is closed and high pressure is slowly built up in the pressure chamber34. The mid-level elevated injection pressure then builds up in the fuel supply line11, which initially causes the first nozzle needle3to open. The slow pressure buildup in the pressure chamber34causes the pressure in the control chamber32to build up, delayed only slightly by the throttle35.

By means of the first control surface43and the coupling sleeve18, a closing needle force less intense than the opening needle force builds up on the first nozzle needle3. By means of the second control surface45, the second needle unit30is subjected to a closing needle force, which, together with the prestressing spring force acting in the closing direction exerted by the closing spring50, is greater than the forces acting on the second needle unit30in the opening direction. As a result, the second nozzle needle4does not open.

In order to close the first nozzle needle3, the valve38is opened so that the relatively mid-level elevated injection pressure in the fuel supply line11is completely discharged. Consequently, the closing forces in the first needle unit17once again predominate, driving the needle unit17in the closing direction21. As soon as the first nozzle needle3has moved into its first seat10, the injection process is terminated. The delayed pressure decrease in the control chamber32here assists the closing motion of the first needle unit17. By means of the first control surface43, the control pressure generates a closing needle force on the first needle unit17, which presses the first nozzle needle3against the first sealing seat10. As the control pressure falls further, the first closing spring20holds the first nozzle needle3against the first sealing seat10and the first control piston41moves into its initial position.

In other operating states of the internal combustion engine, it can be necessary to dispense more fuel at a middle to high elevated injection pressure through both the at least one first injection opening5and the at least one second injection opening6. To this end, the valve38is closed and a middle to high elevated pressure is built up in the pressure chamber34at a relatively middle to high speed. The elevated injection pressure then builds up in the fuel supply line11, which initially causes the first nozzle needle3to open. Then the elevated injection pressure also builds up against the at least one second pressure shoulder27of the second nozzle needle4. The mid-speed to high speed pressure buildup causes the pressure in the control chamber32to build up, but only in a delayed fashion due to the presence of the throttle35, and only a delayed buildup of closing forces occurs via the control surfaces43and45of the control pistons41and42. The opening forces thus generated overcome the closing forces acting on the second needle unit30. Consequently, the second nozzle needle4can also open.

The opening stroke of the second nozzle needle4is limited by a second stroke stop55, which in this instance is embodied between the coupling rod31and the first control piston41, i.e. with a sufficient opening stroke, an axial end surface of the coupling rod31of the second needle unit30comes into contact with the axial end surface of the first control piston41oriented toward it.

Alternatively, the second stroke stop55′ according toFIG. 2can also be embodied on a washer56. The second stroke stop55″ according toFIG. 3can also be embodied directly on the first nozzle needle3.

It is important here that with the buildup of elevated injection pressure at both the relatively slow speed and middle speed, the time delay with which the respective elevated injection pressure also builds up in the control chamber32via the throttle line33is still relatively slight so that only comparatively slight pressure differences arise between the pressure chamber34and the control chamber32. Consequently, the second nozzle needle4reacts comparatively slowly to the increasing pressure against the at least one second pressure shoulder27and opens comparatively late.

There is thus a small to mid-sized pressure difference between the control chamber32and the pressure chamber34so that in order to open the second nozzle needle4, it is necessary to overcome not only the closing force of the second closing spring50, but also an increased closing force engaging the second control surface45due to the increased control pressure in the control chamber32. At low and mid-level elevated injection pressures, the increasing control pressure in the control chamber32consequently counteracts an abrupt opening motion of the second nozzle needle4.

To terminate the injection process, the valve38is opened again so that the mid-level elevated injection pressure in the fuel supply line11is completely discharged. Consequently, the forces acting on both the first needle unit17and the second needle unit30in the closing direction21predominate, as a result of which both of the nozzle needles3and4close. The delayed pressure decrease in the control chamber32assists the closing motion of the two nozzle needles3,4.

In other operating states of the internal combustion engine, it can be necessary to rapidly dispense a large amount of fuel at a relatively high injection pressure into the combustion chamber8through both the at least one first injection opening5and the at least one second injection opening6. For example, this is when the internal combustion engine is running at comparatively high speeds so that in connection with the relatively high injection pressure, it is desirable to achieve both extremely short opening times and extremely short closing times for the two needles3and4.

Here, too, in order to open the nozzle needles3,4, the valve38is closed and the desired, relatively high elevated injection pressure is generated in the pressure chamber34. This high elevated injection pressure spreads through the fuel supply line11to the at least one first pressure shoulder14of the first nozzle needle3. Since the first nozzle needle3is designed so that it opens at a relatively low elevated injection pressure, it reacts immediately and opens very early. After the first nozzle needle3opens, the pressure also increases against the at least one second pressure shoulder27of the second nozzle needle4. As a result, the fuel pressure against the at least one second pressure shoulder27of the second nozzle needle4increases significantly faster than the pressure in the control chamber32, which is connected to the pressure chamber34via the throttle line33. This generates a relatively large pressure difference between the pressure chamber34and the control chamber32in which the throttle connection plays a particularly significant role. The forces acting on the second needle unit30in the closing direction21are essentially limited to the closing force of the second closing spring50and the compression force exerted on the second control surface35by control pressure in the control chamber32, which is still low. Consequently, the high fuel pressure building up against the second pressure shoulder27can very quickly overcome the closing forces of the second needle unit30so that the second needle4also reacts very quickly and opens.

With a sufficiently long opening time, the high injection pressure of the pressure chamber34also spreads into the control chamber32in a delayed fashion via the throttle line33.

If the injection process is then to be terminated, the valve38is opened and the high injection pressure in the pressure chamber34falls. This pressure drop then spreads immediately to the pressure shoulders14and27of the nozzle needles3and4, thus reducing the forces acting in the opening direction on the needle units17and30. At the same time, the throttle35generates a comparatively large pressure difference between the control chamber32and the pressure chamber34so that now, the control pressure of the control chamber32, which is still relatively high, engages both the first control surface43and the second control surface45, consequently imparting powerful closing forces to the first control piston41and the second control piston45.

This causes the first control piston41to move in the closing direction21. If the first control piston41constitutes the second stroke stop55for the second nozzle needle4as it does in this instance, then it carries the second needle unit30along with it. In other instances, it is carried along by the alternative second stroke stop55′ or55″. Moreover, the first control piston41can simultaneously constitute the first stroke stop53for the first nozzle needle3so that during its closing motion, the control piston41also carries the first needle unit17along with it. As long as an axial play remains between the first control piston41and the coupling sleeve18, the first control piston41initially executes a relatively small idle stroke in relation to the first needle unit17and only then does it carry the first needle unit17along with it. The high pressure in the control chamber32can thus abruptly push the two nozzle needles3,4or two needle units17,30in the closing direction21by means of the control pistons41,42, which results in the achievement of very short closing times for the two nozzle needles3,4. The control pressure in the control chamber32is discharged by means of the stroke motion of the control pistons41,42and by means of the throttle35.

The sudden or abrupt acceleration due to the high control pressure acting mainly on the first control surface43and also on the second control surface45overcomes the inertial forces in order to accelerate the needle units17,30, thus permitting the achievement of extremely short closing times, even if the control pressure in the control chamber32decreases due to the axial movement of the first control piston41. It is also important that the extremely short closing times become shorter the higher the respective elevated injection pressure is selected to be. In mid-sized and small changes in the elevated injection pressure, the delay effect due to the throttle line33has either no effect or only an insignificant effect on the increase or decrease of the control pressure in the control chamber32, which is also desirable for the respective operating states of the internal combustion engine. In the injection nozzle1according to the present invention, it is particularly advantageous that both nozzle needles3,4are controlled by means of the injection pressure so that no servo control is required. It is consequently comparatively inexpensive to produce the injection nozzle1according to the present invention.

During the closing of the nozzle needles3and4, in addition to the two needle units17,30, the first control piston41also carries the drive ring22along with it, simultaneously placing the first closing spring20under stress. This increases the closing force of the first closing spring20so that as the closing force of the first control piston41slackens, an increased closing force still continues to act on the first needle unit17in order to close the first nozzle needle3as fast as possible. A rapid closing of the first nozzle needle3is of primary importance for a rapid termination of the injection process. This is so because as soon as the first nozzle needle3is closed, the at least one second injection opening6is also disconnected from the fuel supply, thus terminating the introduction of fuel through the at least one second injection opening6, even if the second nozzle needle4has not yet traveled into the second sealing seat26.

As soon as the throttle line33has caused the control pressure to decrease sufficiently, the first closing spring20, acting via the drive ring22, can push the first control piston41back into its initial position according toFIG. 1. The end of the return motion is reached when the drive ring22comes into contact with the stop sleeve23and this comes into contact with the shoulder24.