| Title of Invention | A FUEL INJECTION NOZZLE WITH A NOZZLE BODY |
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| Abstract | In a fuel injection nozzle with a nozzle body (10), a nozzle needle (12), which is dispplaceable in the nozzle body, a piezoelectric actuator (20), which is connected to the nozzle needle, and a compensating piston (30), against which the piezoelectric actuator is supported and which projects into a compensating chamber (32), which is filled with a fluid, the compensating chamber being connected to a supply volume (34) by an inlet of small cross section, ithe aim is to achieve a simpler structure. For this purpose, the supply volume (34) is subjected to a variable pressure, In this way, it is possible to dispense with a separate return spring for the nozzle needle. |
| Full Text | The invention relates to a fuel injection nozzle with a nozzle body. An injection nozzle of this kind is known from DE 35 33 085 Al. The compensating piston makes it possible to compensate for a slow change in the length of the piezoelectric actuator. Such a change in length is caused, in particular, by a change in temperature. When such a change occurs, the fluid is displaced froth the compensating chamber or drawn into the latter by the compensating piston. If, on the other hand, a rapid change in the length of the piezoelectric actuator occurs, such as that brought about to open the nozzle needle, the resistance to any displacement of the fluid in the compensating chamber is so great owing to the small cross section of the inlet that the compensating piston acts as a rigid abutment. The nozzle needle can then be actuated without the compensating piston affecting the opening stroke brought about. With the known injection nozzle, which is an outward-opening nozzle, a separate return spring is provided for the nozzle needle. To open the nozzle needle, it is necessary for the piezoelectric actuator to overcome the force exerted by the return spring, leading to high actuating forces. The object of the invention is to provide a fuel injection nozzle that does not require the return spring that must be overcome by the piezoelectric actuator. Advantages of the invention : A fuel injection nozzle of the type as described herein, has the advantage that the pressure prevailing in the supply volume, which also acts on the compensating piston, acts in a manner similar to a return spring for the nozzle needle, thus making it possible to dispense with the separate, highly preloaded return spring. Accordingly, the present invention provides a fuel injection nozzle with a nozzle body, a nozzle needle, which is displaceable in the nozzle body, a piezoelectric actuator, which is connected to the nozzle needle, and a compensating piston, against which the piezoelectric actuator is supported and which projects into a compensating chamber, which is filled with a fluid, the compensating chamber being connected to a supply volume by an inlet of small cross section, characterized in that the supply volume is subjected to a variable pressure. Advantageous refinements of the invention are described herein. Drawings : The invention is described below with reference to a preferred embodiment, which is illustrated in Figure 1 of the attached drawing. In this drawing, a fuel injection nozzle according to the invention is shown in a schematic section. Description of the exemplary embodiment: The illustration according to Figure 1 reveals that the injection nozzle has a nozzle body 10, in which an inward-opening nozzle needle 12 is arranged in a displaceable manner. The nozzle needle 12 can open spray holes 14, which are formed in the nozzle body 10, to enable the injection of fuel, which is provided via a feed hole 16 and an annular passage 18. The feed hole 16 is supplied by a common high-pressure line, which is known by the name "common rail". At its end remote from the spray holes 14, the nozzle needle 12 is connected to a piezoelectric actuator 20, which comprises a stack of piezoelectric elements 22 and a holder 24. The piezoelectric elements are preloaded in the holder 24 by an annular spring 26. The piezoelectric actuator 20 is furthermore provided with supply connections (not shown), by means of which a voltage can be applied to the piezoelectric elements 22, Arranged at that end of the piezoelectric actuator 20, which is remote from the spray holes 14 there is a ball 28, against which a compensating piston 30 rests. The ball 28 ensures that any tolerances and deviations in position between the compensating piston 30 and the piezoelectric actuator 2 0 in the radial direction are not transmitted from one component to the other. The piston 3 0 projects into a compensating chamber 32, which is connected to a supply volume 34 via an annular gap of thickness d between the wall of the compensating chamber 32 and the compensating piston 30. The supply volume is under the system pressure PSYS, which is generally equal to the pressure of the fuel supplied. Arranged between the nozzle body 10 and a collar of the compensating piston 30 is a compression spring 36, which presses the compensating piston 30 against the piezoelectric actuator 20. The compression spring 36 thus acts on the compensating piston 3 0 in such a way that there is a tendency for the volume of the compensating chamber 32 to increase. The fuel injection nozzle described operates in the following manner: when the injection system associated with the injection nozzle is switched off, the compression spring 36 ensures that the nozzle needle 12 is pressed into contact with the nozzle body 10 by means of the piezoelectric actuator 20, with the result that the spray holes 14 are closed and no fuel can enter the combustion chamber of an internal combustion engine to be supplied from the injection nozzle. If, on the other hand, the injection system is switched on and fuel under system pressure is being supplied via the feed hole 16, an opening force is produced on the annular shoulder of the nozzle needle 12, said annular shoulder being arranged in the annular chamber 18. This force pushes the nozzle needle 12 upward in the figure. The piezoelectric actuator 20 and the compensating piston 30 counteract the opening force, A voltage is applied to the piezoelectric elements 22 in the compensating state, with the result that the individual piezoelectric elements lengthen axially. In this state the rear end of the piezoelectric actuator" 20 is supported via the compensating piston 3 0 against the fluid, which is under system pressure in the compensating chamber 32, When the nozzle needle 12 is to be opened, the voltage applied to the piezoelectric elements 22 is interrupted. The piezoelectric elements then contract axially, enabling the nozzle needle 12 to perform an opening stroke of up to 0.25 mm. During this movement, the compensating piston 3 0 remains in position since the fluid in the compensating chamber 32 does not allow movement of the compensating piston 30; the annular gap around the compensating piston 30, through which additional fluid could flow out of the supply volume 34, is so small that, for the short periods during which the nozzle needle is open, the system can be assumed to be fixed. When the nozzle needle is to be closed again, the voltage is reapplied to the piezoelectric elements 22, with the result that they expand in the axial direction and displace the nozzle needle 12 into its closed position. If, on the other hand, a change in the length of the components of the injection nozzle, especially of the piezoelectric actuator, during a change in temperature occurs during the operation of the injection nozzle, this leads to a corresponding displacement of the compensating piston 3 0 in the compensating chamber 32, the fluid either being displaced out of the compensating chamber 32 or drawn into it through the annular gap of thickness d. WE CLAIM : 1. A fuel injection nozzle with a nozzle body (10), a nozzle needle (12), which is displaceable in the nozzle body, a piezoelectric actuator (20), which is connected to the nozzle needle, and a compensating piston (30) , against which the piezoelectric actuator is supported and which projects into a compensating chamber (32), which is filled with a fluid, the compensating chamber being connected to a supply volume (34) by an inlet of small cross section, characterized in that the supply volume (34) is subjected to a variable pressure. 2. The injection nozzle as claimed in claim 1, wherein the supply volume (34) is at the pressure of the fuel to be injected. 3. The injection nozzle as claimed in claims 1 and 2, wherein the supply volume (34) is filled with fuel. 4. The injection nozzle as claimed in any one of the preceding claims, wherein a spring (36) that engages on the piezoelectric actuator (20) and pushes the nozzle needle (12) into its closed position is provided, 5. The injection nozzle as claimed in any one of the preceding claims, wherein a ball (28) is arranged between the compensating piston and the piezoelectric actuator, enabling tolerance compensation between the compensating piston and the piezoelectric actuator. 6. A fuel injection nozzle with a nozzle body, substantially as hereinabove described and illustrated with reference to the accompanying drawings. |
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| Patent Number | 212762 | ||||||||
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| Indian Patent Application Number | IN/PCT/2001/1116/CHE | ||||||||
| PG Journal Number | 07/2008 | ||||||||
| Publication Date | 15-Feb-2008 | ||||||||
| Grant Date | 14-Dec-2007 | ||||||||
| Date of Filing | 07-Aug-2001 | ||||||||
| Name of Patentee | ROBERT BOSCH GMBH | ||||||||
| Applicant Address | Postfach 30 02 20 70442 Stuttgart | ||||||||
Inventors:
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| PCT International Classification Number | F02M 51/06 | ||||||||
| PCT International Application Number | PCT/DE2000/003694 | ||||||||
| PCT International Filing date | 2000-10-20 | ||||||||
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