Diesel Common-Rail Piezo-Operated Servo Injector

Abstract

Various embodiments may include a method for operating a diesel-common-rail piezo-operated servo injector comprising: partially charging the piezo-actuator from a non-charged state at 0 V (method a); partially discharging the piezo-actuator from an already charged state to a remaining limited charge (method b); measuring the piezo-voltage with both methods and comparing the results; when the comparison demonstrates correspondence within a predefined threshold, using method b in ranges in which method a cannot be carried out; and when the comparison does not demonstrate correspondence within the predefined threshold, using method a without using method b.

Claims

1. A method for operating a diesel-common-rail piezo-operated servo injector in which a piezo-actuator opens and closes a nozzle needle by means of a servo valve, the method comprising: partially charging the piezo-actuator from a non-charged state at 0 V (method a); partially discharging the piezo-actuator from an already charged state to a remaining limited charge (method b); measuring the piezo-voltage with both methods and comparing the results; determining a voltage for the piezo-actuator for each operating point so that the piezo-actuator applies a force necessary for contact with the servo valve without influencing the injection process itself by opening the servo valve; when the comparison demonstrates correspondence within a predefined threshold, using method b in ranges in which method a cannot be carried out; and when the comparison does not demonstrate correspondence within the predefined threshold, using method a without using method b.

2. The method as claimed in claim 1, further comprising switching to and fro between method a and method b during a specific injection process throughout one engine cycle.

3. The method as claimed in claim 1, further comprising measuring the force during a specific main injection.

4. The method as claimed in claim 1, further comprising measuring the force during times at which no large change of the operating point takes place.

5. The method as claimed in claim 1, further comprising carrying out the partial discharging of the piezo-actuator (method b) starting from a charged state of said piezo-actuator associated with an actual injection.

6. The method as claimed in claim 1, further comprising executing the partial charging (method a) after complete discharging of the piezo-actuator.

7. A motor vehicle comprising: a combustion chamber; a diesel-common-rail piezo-operated servo injector operating to inject fuel into the combustion chamber; and a control unit programmed to: partially charge the piezo-actuator from a non-charged state at 0 V (method a); partially discharge the piezo-actuator from an already charged state to a remaining limited charge (method b); measure the piezo-voltage with both methods and comparing the results; determine a voltage for the piezo-actuator for each operating point so that the piezo-actuator applies a force necessary for contact with the servo valve without influencing the injection process itself by opening the servo valve; when the comparison demonstrates correspondence within a predefined threshold, use method b in ranges in which method a cannot be carried out; and when the comparison does not demonstrate correspondence within the predefined threshold, use method a without using method b.

Description

[0018] The invention is explained in detail below with reference to an exemplary embodiment in connection with the drawing. In the drawing:

[0019] FIG. 1 shows a diagram which clarifies method variant a;

[0020] FIG. 2 shows a diagram which illustrates method variant b; and

[0021] FIG. 3 shows a diagram which shows the sequence of the method according to the invention in three illustrations.

[0022] In the case of the method described here for operating a diesel-common-rail piezo-operated servo injector, the piezo-actuator is actuated as a sensor in order to measure the force applied to the servo valve. In order to be able to carry out the corresponding force measurement, the correct quantity of charge for the piezo-actuator must be determined so that said piezo-actuator brings about the force contact, necessary for the force measurement, with the servo valve without influencing the injection process itself by opening the servo valve. In other words, the piezo-actuator has to overcome the air gap, present in the non-charged state, between the actuator and the servo valve.

[0023] For this purpose, according to the method a illustrated in FIG. 1, the piezo-actuator is partially charged from a non-charged state at 0 V. In FIG. 1, the corresponding piezo-voltage is illustrated as a function of the time, wherein an injection pulse of a main injection and a subsequent auxiliary detection pulse for partial charging are illustrated. The possible measuring window for carrying out the method a is shown to the right of the dashed line.

[0024] In the method b illustrated in FIG. 2, partial discharging of the piezo-actuator from an already charged state (injection pulse) to a remaining charge takes place. Here, the injection pulse and the auxiliary detection pulse according to method variant b are also illustrated. It is apparent that the possible measuring window indicated to the right of the dashed line is larger here than in the case of method a.

[0025] FIG. 3 shows the execution of the method according to the invention in which, during a specific injection process, switching to and fro between method a and method b is carried out periodically for one engine cycle. In the left-hand diagram, method a is illustrated for cycle n, in the middle diagram method b is illustrated for cycle n+1, and in the right-hand diagram method a is illustrated again for cycle n+2. In the diagrams, an injection pulse and an auxiliary detection pulse are also illustrated in each case for the corresponding method.

[0026] The piezo-voltage at the piezo-actuator is measured with both methods, and the results are compared with one another. When there is sufficient correspondence, method b is carried out in ranges in which method a cannot be carried out. When there is not sufficient correspondence no application of method b takes place.