Method, program product, and computer for estimating static flow rate of piezoelectric injector

Abstract

The present invention relates to a method for determining the static flow rate of a piezoelectric injector of an injection system (2). The piezoelectric injector (5) comprises a needle and a piezoelectric actuator which is designed to control the valve of the injector (5). The injection system (2) comprises a generator (8) and a voltage sensor, the generator being designed to send current pulses to the piezoelectric actuator of the injector (5), and the voltage sensor being designed to measure the voltage value at the terminals of the piezoelectric actuator. The method comprises the following steps: - sending a current pulse during the closing phase of the needle such that the piezoelectric actuator is positioned in contact with the valve without causing the valve to open; - measuring a plurality of voltage values of the piezoelectric actuator; and - determining the static flow rate of the piezoelectric injector (5) based on the plurality of measured voltage values of the piezoelectric actuator.

Description

Technical Field

[0001] The present invention relates to a method for controlling an engine, and more particularly to a method for controlling an injector in a combustion engine. The present invention is more particularly applied to the motor vehicle industry. Background Art

[0002] Traditionally, an injection engine includes an injector provided with injection holes and a rail for supplying fuel to the injector. These injectors are designed to inject fuel into the combustion chamber via said holes, the fuel being subjected to a determined pressure in the rail by means of a high-pressure pump. In each injector, a needle (aiguille) is used to perform the opening and closing of the injection holes located at the end of the injector, this end being designed to be located in the combustion chamber, said end sometimes being referred to as the "nose" (nez) of the injector.

[0003] Due to their use, injectors are affected by corrosion and fouling phenomena, which cause a change in their static flow rate.

[0004] In this context, the "static flow rate of an injector" means the flow rate of fuel supplied by the injector to the combustion chamber at a determined pressure after the needle of the injector has been opened, the opening time being long enough to establish a substantially constant instantaneous flow rate of the supplied fuel. Figure 1 represents three instantaneous flow rate curves of the injector on the y-axis d during the opening and closing cycles of the corresponding needle of the injector during the time on the x-axis t. On each of these curves, a plateau can be seen to form at the top of the instantaneous flow rate curve, which corresponds to a substantially constant flow rate value and thus represents the static flow rate of the injector.

[0005] Curve P1 is shown in Figure 1 and corresponds to the response of a corroded injector during the opening and closing cycles of its needle. It can be seen that corroded injectors are characterized in that their holes are wider compared to the original diameter of the holes of the injector at the outlet of the production line, which results in an increase in the static flow rate of said injectors. In this case, corrosion causes a reduction in the pressure loss (perte de charge) at the front end of the injector during fuel injection. This pressure loss constitutes a pressure difference that exists between the fuel pressure in the chamber containing the front end of the injector and the pressure at the outlet of said front end. The reduction in pressure loss causes the needle of the corroded injector to open, which is earlier than that of a nominal injector that has not experienced a reduction in pressure loss (by Figure 1The opening of the curve P0 (represented in []) is slower. The closing of the needle is also faster than that of the nominal injector because, as the needle is opened more slowly, it is lifted less high than the needle of the nominal injector and thus closes faster than the needle of the nominal injector. In addition, the pressure at the base of the needle of the corroded injector is lower than that of the nominal injector because of the lower pressure loss during injection, and thus the closing resistance of the needle of the corroded injector is lower than that of the nominal injector, and thus the needle closes again at a higher speed. The increase in the static flow rate of the injector causes a harmful increase in the amount of fuel injected during the opening and closing cycles of the needle, and thus causes an increase in the emission of polluting gases and causes a drift in the engine torque.

[0006] On the other hand, the curve P2 in Figure 1 represents a dirty injector, the holes of which are partially blocked by material, resulting in a reduction in the static flow rate of the injector. In this case, the opening of the needle of the dirty injector is faster than that of the nominal injector because of the increase in the pressure loss associated with the front end of the injector due to the dirt. The closing of the needle is also slower than that of the nominal injector. In fact, since the needle is opened faster, the needle is lifted higher than the needle of the nominal injector, and the increase in the pressure loss means that the closing resistance of the needle of this injector is greater than the closing resistance of the needle of the nominal injector, and thus the needle closes more slowly. In particular, the reduction in the static flow rate of the injector causes a drift in the engine torque.

[0007] Therefore, it can be understood that knowing the static flow rate of the injector makes it possible to at least partially adjust the above negative effects. For example, knowing the static flow rate of the injector makes it possible to generate an alarm in the case of a large deviation from the nominal static flow rate value to correct the pressure in the supply rail or also to correct the injection electrical command.

[0008] A variety of known methods make it possible to estimate the static flow rate of the injector.

[0009] Some of these known methods are based on the low pressure observed in the fuel supply rail during fuel injection, in the analysis of the crankshaft sensor or in the analysis of the concentration sensor. However, these methods present problems of accuracy in estimating the static flow rate, and these methods depend on parameters unrelated to the injector, such as the pressure disturbance in the rail for the method based on low pressure, or the engine performance, and the dependence on the transmission chain and the intake pressure for the methods based on data from the crankshaft sensor or from the concentration sensor.

[0010] Other known methods use additional sensors, such as pressure sensors in the control room of a servo-driven injector, optical sensors, sensors via electrical contact between the needle and the front end of the injector, or cylindrical pressure sensors in the combustion chamber. Adding additional sensors makes the system more complex and expensive. In fact, in addition to the inherent price of the sensors, their reliability must be considered, and their failure modes must be controlled.

[0011] There are also solutions as follows: These solutions are based on the relationship between the predetermined closing moment of the injector needle and the static flow rate drift. However, the actual closing of the needle depends on various other influences, such as the dependence of the pressure wave obtained from the previous injection on multiple injections, or in the case of a piezoelectric injector, the dependence on the opening control of the valve controlled by the piezoelectric actuator. Therefore, these solutions are difficult to implement and lack precision.

[0012] Therefore, the present application seeks to solve the problems brought about by the methods according to the prior art. Summary of the Invention

[0013] Therefore, the first object of the present application is to propose a method for estimating the static flow rate of a piezoelectric injector in a combustion engine.

[0014] The second object includes implementing such a method on the injection system without modifying it, in particular without adding auxiliary sensors.

[0015] The third object of the present invention is to make the estimation of the static flow rate robust with respect to multiple injections and the opening control of the piezoelectric injector valve.

[0016] The fourth object of the present invention includes generating an alarm when the determined static flow rate of the piezoelectric injector is greater than a predetermined threshold.

[0017] Finally, the fifth object includes correcting the fuel quantity injected by the injector according to the determined static flow rate.

[0018] In this regard, the present invention proposes a method for determining the static flow rate of a piezoelectric injector of an injection system of a combustion engine, the piezoelectric injector including a needle and a piezoelectric actuator, the piezoelectric actuator being designed to control the valve of the injector, the injection system including a generator and a voltage sensor, the generator being designed to send a current pulse to the piezoelectric actuator of the injector, the voltage sensor being designed to measure the voltage value at the terminals of the piezoelectric actuator,

[0019] The method is characterized in that it includes the following steps:

[0020] - Sending a current pulse from the generator to the piezoelectric actuator such that the piezoelectric actuator is positioned in contact with the valve without causing the valve to open, and the sending is performed during the closing of the needle;

[0021] - Measuring a plurality of voltage values of the piezoelectric actuator by a voltage sensor; and

[0022] - Determining a static flow rate of the piezoelectric injector based on the measured plurality of voltage values of the piezoelectric actuator.

[0023] According to an alternative, the step of determining the static flow rate includes calculating a time t when the piezoelectric actuator contacts the valve after a current pulse has been sent c and a time t after the needle closing time t3 end for a first sub-step of voltage change dV therebetween.

[0024] In this alternative, the step of determining the static flow rate may further include a second sub-step of calculating a pressure change dP in the injector control chamber based on the voltage change dV at the electro-actuator terminals cc thereof.

[0025] In this alternative, the step of determining the static flow rate may further include a third sub-step of determining the static flow rate of the injector based on a table of the voltage change dV and a static flow rate reference value of the piezoelectric injector.

[0026] According to an alternative, the method is only implemented when:

[0027] - A determined duration between the valve closing time t2 and the needle closing time t3 is greater than a predetermined threshold; and

[0028] - The temperature of the engine is between a first predetermined temperature and a second predetermined temperature; and

[0029] - The engine speed is between a first predetermined rotational speed and a second predetermined rotational speed.

[0030] According to an alternative, the method includes a supplementary step of generating an alarm when an absolute value of a difference between the determined static flow rate of the injector and a nominal static flow rate of the injector is greater than a predetermined threshold.

[0031] According to an alternative, the injection system further includes a fuel supply rail, and controls the fuel pressure in the fuel supply rail according to the static flow rate of the injector.

[0032] The present invention further includes a computer program product including encoded instructions for implementing the above method steps.

[0033] The present invention also proposes a computer designed to control a combustion engine injection system including a piezoelectric injector, the injector including a needle and a piezoelectric actuator, the piezoelectric actuator being designed to control a valve of the injector,

[0034] The injection system further comprises: a generator designed to send current pulses to the piezoelectric actuator of the injector; a voltage sensor designed to measure the voltage value at the terminals of the piezoelectric actuator; and a fuel supply rail, and the computer is also designed to control the implementation of the steps of the above method.

[0035] The computer can also be incorporated into a combustion engine having an injection system as described above.

[0036] Thus, the method proposed according to the present invention makes it possible to estimate the static flow rate of the piezoelectric injector in the combustion engine based on the voltage value at the terminals of the piezoelectric actuator. Thus, the method can be implemented without modifying the existing engine injection system and thus does not make it more complex, for example by adding auxiliary sensors. Since the method is not based on a predetermined closing moment of the needle, it is not affected by the transients that change the needle closing (which are not caused by the static flow rate), and in particular those related to multiple injections, the opening control of the valve of the piezoelectric injector or the aging of the injector. Thus, the method makes it possible to trigger an alarm when the static flow rate of the injector is greater than a predetermined threshold, or to control the amount of fuel injected into the engine combustion chamber by controlling the pressure of the fuel in the supply rail. Description of the Drawings

[0037] Other features, details and advantages will become apparent by reading the following detailed description and analyzing the accompanying drawings, in which:

[0038] Figure 1 Figure 1 shows three instantaneous flow rate curves of the injectors during the opening and closing cycles of their respective needles.

[0039] Figure 2 Figure 2 shows an embodiment of an injection system for implementing a method for determining the static flow rate of a piezoelectric injector.

[0040] Figure 3 Figure 3 shows an embodiment of a method for determining the static flow rate of a piezoelectric injector.

[0041] Figure 4a Figure 4a shows a piezoelectric injector during the injection phase.

[0042] Figure 4b Figure 4b shows Figure 4a an enlarged view of the valve, piezoelectric actuator and control chamber of the piezoelectric injector.

[0043] Figure 5 Figure 5 ​​​​​​shows three graphs related to the elements of a piezoelectric injector during the opening and closing cycles of the injector needle.

[0044] The upper graph shows the voltage on the piezoelectric actuator terminals and the opening degree of the valve controlled by the actuator during the cycle.

[0045] The middle graph shows the pressure in the injector control chamber during the cycle.

[0046] The lower graph shows the needle stroke during the cycle.

[0047] Figure 6 Figure 6 also shows three graphs related to the elements of a piezoelectric injector during the opening and closing cycles of the injector needle, and incorporates the Figure 3 method shown in

[0048] The upper graph shows the voltage on the piezoelectric actuator terminals and the opening degree of the valve controlled by the actuator during the cycle.

[0049] The middle graph shows the pressure in the injector control chamber during the cycle.

[0050] The lower graph shows the opening of the needle during the cycle.

[0051] Figure 7 Figure 7 shows an embodiment of the steps for determining the static flow rate based on a plurality of voltage values measured at the terminals of a piezoelectric actuator. Detailed Description

[0052] Now refer to Figure 2 , which shows an embodiment of an injection system 2 for a combustion engine (such as a motor vehicle engine). This injection system 2 allows the implementation of the Figure 3 method shown in

[0053] The injection system 2 includes a fuel supply rail 4, which is connected to a fuel tank (not shown) through a supply line. In addition, the fuel tank is also connected to a plurality of piezoelectric injectors 5 through a return line. The fuel present in the supply rail 4 is supplied at a determined pressure by a high-pressure pump 9 to contribute to the good combustion of the fuel during different injection phases. Therefore, it follows a set pressure determined by an engine computer (not shown), which controls the high-pressure pump 9. The engine computer can be, for example, a processor, a microprocessor, or a microcontroller. The engine computer can also have a memory that includes encoded instructions to control the Figure 3 ​​The implementation of the steps of the method for determining the static flow rate of a piezoelectric injector as shown. The injection system 2 also includes a generator 8.

[0054] In Figure 4a and 4b the piezoelectric injector 5 of the injection system 2 is shown more specifically. It includes: a high-pressure fuel inlet 501; a low-pressure fuel outlet 502, which leads to the return line of the injector 5 and thus to the fuel tank; and a front end, which includes a plurality of holes 503 for injecting fuel into the engine combustion chamber (not shown). The injector also includes a needle 53, which can move in a chamber at the front end of the injector 530, the chamber at the front end being in fluid communication with the high-pressure fuel inlet 501. The needle 53 can move between a first position and a second position, where in the first position, the needle 53 closes the fuel injection holes 503, and in the second position, the needle 53 opens these holes ( Figure 4a and 4b the positions shown), thus allowing fuel to be injected into the combustion chamber. The needle 53 is held in the closed position by a return spring 535.

[0055] The injector 5 also includes a control chamber 54 (see Figure 4b ), the control chamber 54 being located at the end of the needle 53 opposite to the front end of the injector. The control chamber 54 is in fluid communication with the high-pressure fuel inlet 501 via a narrowing 540, and is in fluid communication with the low-pressure fuel outlet 502 leading to the fuel tank via a second narrowing 541 and a valve 52, where the valve 52 is located between the outlet 502 and the second narrowing 541.

[0056] In this case, the pressure P in the control chamber 54 cc and the pressure P in the chamber at the front end of the injector 530 a make it possible to open or close the needle 53 of the injector. When the needle 53 and the valve 52 of the injector 5 are closed, the pressure P in the control chamber 54 cc is equal to the fuel pressure in the fuel supply rail 4. In this regard, the difference between the pressures P cc and P a is zero. Therefore, the sum of the forces generated by the sectional difference applied by the pressures P cc and P a , the force applied by the return spring 535, and the weight of the needle keep the needle 53 of the injector closed.

[0057] The injector also includes a piezoelectric actuator 51. When the piezoelectric actuator 51 receives a first electrical pulse from the generator 8 of the injection system 2, the piezoelectric actuator 51 is charged and elongates by the piezoelectric effect, thus being supported on the valve 52. As Figure 4a and 4bAs shown, the valve 52 is supported with sufficient force to allow fluid to circulate from the high pressure fuel circuit of the injector to the low pressure outlet 502. This causes the pressure P in the control chamber 54 to cc decreases, and thus causes the needle 53 to be at a high pressure P a The high pressure P a The fuel is retained in the chamber at the front end of the injector 530, thereby opening the injection hole 503. Thus, the fuel can move from the supply rail 4 toward the combustion chamber via the injection hole 503 and thus trigger the injection into the combustion chamber. The purpose is therefore to open the needle 53 by charging the piezoelectric actuator 51 of the piezoelectric injector.

[0058] In order to close the needle 53 and thus interrupt the injection phase, the generator 8 sends a second electrical pulse to the piezoelectric actuator 51 of the injector 5 in order to discharge the piezoelectric actuator 51. When it is discharged, the piezoelectric actuator 51 retracts and therefore no longer bears on the valve 52 with sufficient force to keep the valve open. The valve 52 is therefore closed and the pressure P in the control chamber 54 is reduced. cc and the pressure P in the chamber at the front end of the ejector 530 a The balance is reversed and needle 53 is closed again.

[0059] However, the closing of the needle is not immediate and therefore there is a certain inertia period of the needle 53 between the closing instant t2 of the valve 52 and the closing instant t3 of the needle 53 .

[0060] The opening and closing cycle of the needle 53 of the piezoelectric injector 5 is shown during an injection cycle which causes the different elements of the piezoelectric injector 5 to intervene and which are shown previously in [ Figure 5 ] is the time specified in .

[0061] Thus, the top diagram shows the voltage V at the terminals of the piezoelectric actuator 51 of the injector, and the opening Ov of the valve 52 of the injector 5 as a function of time t. The middle diagram also shows the pressure P in the control chamber 54 as a function of time t. cc Finally, the bottom diagram shows the opening Oa of the needle 53 of the piezo injector 5 as a function of time. It should be understood that the time reference in the three diagrams is the same.

[0062] When the valve 52 is opened at time t0, the pressure P in the control chamber 54 is observed to be cc decreases because the chamber is in fluid communication with the low pressure outlet 205 of the injector 5. This causes the needle 53 to begin to open at time t1, when the pressure P a The resultant force on the cross section of the base of the needle 53 becomes greater than the sum of the forces applied at the top of the needle 53, i.e., the pressure P applied on the cross section of the top of the needle. ccThe sum of the forces generated, the force applied by the return spring 535, and the force applied due to the weight of the needle 53.

[0063] On the other hand, when the valve closes at time t2, the pressure P in the control chamber 54 is observed cc to increase because the chamber is no longer in communication with the low-pressure outlet 205 of the injector 5. The pressure level in the control chamber 54 is established at an intermediate value between the pressure when the valve 52 is open and the pressure in the fuel supply rail 4 because, at this stage, the needle 53 is still open. This causes the needle 53 to start closing because the resultant force of the forces applied in the closing direction (the force applied by the return spring 535, the pressure P applied to the top cross-section of the needle 53 in the control chamber 54 cc and the gravitational force on the needle 53) becomes greater than the force generated by the pressure P a applied to the base cross-section of the needle 53 in the chamber at the front end of the injector 530.

[0064] In this case, the aim is to present the normal operation of the piezoelectric injector in order to be able to describe a method for determining the static flow rate of the piezoelectric injector.

[0065] Reference Figure 3 , an embodiment of a method for determining the static flow rate of a piezoelectric injector is given below. Reference will also be made to Figure 6 during the description of the method.

[0066] The method comprises a first step 110: sending a current pulse from the generator 8 to the piezoelectric actuator 51 such that the piezoelectric actuator 51 is positioned in contact with the valve 52 without causing the valve 52 to open. This step is carried out when the needle 53 of the piezoelectric injector 5 closes again during the injection phase. More specifically, during the injection phase, this step is carried out at a time t1 between the closing time t2 of the valve 52 and the closing time t3 of the needle 53. In this case, this step is carried out when the needle 53 of the piezoelectric injector closes again, and thus the aim is to position the piezoelectric actuator 51 in contact with the valve 52, but not to open the valve 52 again. The opening of the valve 52 can be caused by a new inversion of the pressures P cc and P a in the chamber, which causes the needle 53 to rise and would change the operation of the injector.

[0067] The aim of the remainder of the method is to use the piezoelectric actuator 51 as a pressure change sensor in the control chamber 54.

[0068] Thus, the method includes a second step 120: measuring a plurality of voltage values of the piezoelectric actuator 51 by a voltage sensor (not shown). The plurality of voltage values can be measured continuously during the entire injection phase of the piezoelectric injector 5, and the static flow rate of the piezoelectric injector 5 will be estimated. Advantageously, the measurement of the voltage values among the plurality of voltage values can be performed between a moment t1 and a moment t after the closing moment t3 of the needle 53. During the moment t1, a current pulse is sent by the generator 8, and the moment t is far enough to allow a stable pressure P to be established in the control chamber 54 of the injector 5. end between, during the moment t1, a current pulse is sent by the generator 8, and the moment t end is far enough to allow a stable pressure P to be established in the control chamber 54 of the injector 5 cc .

[0069] The method then includes a third stage 130: determining the static flow rate of the piezoelectric injector 5 based on the measured plurality of voltage values of the piezoelectric actuator 51.

[0070] As Figure 6 shown, when the needle 53 of the injector 5 is re-closed at the moment t3, the pressure P in the control chamber 54 cc increases because the fuel circuit from the supply rail 4 and passing through the piezoelectric injector 5 becomes sealed again, and thus is again subject to the fuel pressure of the supply rail 4 provided by the high-pressure pump 9. Therefore, the force applied to the closed valve 52 increases, and when the piezoelectric actuator 51 contacts the valve 52, the voltage V of the actuator 51 thus increases in response to the increase in pressure P in the control chamber 54. These phenomena are marked with circles in cc . Figure 6 .

[0071] In addition, in Figure 6 , three different piezoelectric injector responses are shown. The curve corresponding to the nominal injector is shown as a thick solid line on each graph. When the operation of the corroded injector is different from that of the nominal injector, the curve corresponding to the corroded injector is shown as a broken line on each graph. When the operation of the dirty injector is different from that of the nominal injector, the curve corresponding to the dirty injector is shown as a dotted line on each graph.

[0072] Figure 6 It shows that there is a direct correlation between the change dV of the voltage V at the terminals of the piezoelectric actuator 51 and the change dP of the pressure P in the control chamber 54 when the needle 53 of the injector is closed. In addition, considering that between the moments t2 and t3, the fuel only flows through the injection holes 503, and after the moment t3, the system is sealed again, it is known that there is also a correlation between the change dP of the pressure in the control chamber 54 caused by the closing of the needle 53 and the static flow rate of the injector 5. cc of the pressure P cc and the static flow rate of the injector 5. cc and the static flow rate of the injector 5.

[0073] In this case, when the needle 53 is closed, the pressure change dP in the control chamber 54 cc is greater, the static flow rate of the piezoelectric injector 5 is greater. In fact, when the static flow rate of the injector is large and the needle 53 is open, the pressure difference (or load difference) between the pressure accumulated at the front end of the injector 5 and in particular at the orifice 503 of the injector 5 and the fuel pressure discharged into the combustion chamber through said orifice is low. This means that before being discharged into the combustion chamber, the fuel does not accumulate significantly at the orifice 503 but easily leaves from the front end of the injector 5. This actually means that the fuel passage cross-section of the orifice 503 is large, so that the fuel does not accumulate at said orifice and cannot be discharged. In particular, this is the case of a corroded injector, due to corrosion, the passage cross-section of the corroded injector at the orifice 503 is larger than that of the nominal injector.

[0074] As a result, as Figure 6 shown, when the needle 53 of the corroded injector is opened at time t1, the pressure P in the control chamber 54 cc drops more than that of the nominal injector, because it is related to the pressure drop at the front end of the injector, which is the result of the fluid communication between the control chamber 54 and the front end of the injector. However, after the needle 53 is opened, the fuel accumulation at the front end of the corroded injector is less than that at the front end of the nominal injector, because the passage cross-section of the orifice of the corroded injector is larger than that of the orifice of the nominal injector. This means that after the needle is opened, the pressure at the front end of the corroded injector is less than that at the front end of the nominal injector, because the fuel enters the combustion chamber more easily from the front end. Therefore, the pressure drop generated by the opening of the needle is greater at the front end of the corroded injector than at the front end of the nominal injector. Therefore, it can be understood that when the needle 53 is closed at time t3, when the control chamber 54 returns to the fuel pressure level of the supply rail 4, the pressure change dP in the control chamber 54 cc is greater for the corroded injector than for the nominal injector.

[0075] For a dirty injector, the reverse reasoning applies. Therefore, due to fouling, the passage cross-section of the orifice 503 of the dirty injector is smaller than that of the nominal injector.

[0076] Therefore, as Figure 6 shown, when the needle 53 of the dirty injector is opened at time t1, the pressure P in the control chamber 54 ccThe pressure drop is lower than that of the nominal injector because it is related to the pressure drop at the front end of the injector, which is because there is fluid communication between the control chamber 54 and the front end of the injector. However, when the needle 53 is open, the pressure drop at the front end of the dirty injector is less than that at the front end of the nominal injector. In fact, since the cross-sectional area of the passage of the holes of the dirty injector is smaller than that of the holes of the nominal injector, the fuel accumulation at the front end of the corroded injector is greater than that at the front end of the nominal injector. Therefore, this means that the pressure at the front end of the dirty injector is greater than that at the front end of the nominal injector. Therefore, the pressure drop generated by the opening of the needle is smaller at the front end of the dirty injector than at the front end of the nominal injector. Therefore, it can be understood that when the needle 53 is closed at time t3, when the control chamber 54 returns to the fuel pressure level of the supply rail 4, the pressure change dP in the control chamber 54 cc is smaller for the dirty injector than for the nominal injector.

[0077] Therefore, when a plurality of voltage values are measured at the terminals of the piezoelectric actuator 51 of the injector, the voltage change dV characterizes the pressure change dP of the control chamber 54 cc , so that the static flow rate of the piezoelectric injector 5 can be determined.

[0078] Now refer to Figure 7 , and now an embodiment of step 130 for determining the static flow rate of the piezoelectric injector 5 will be described.

[0079] Determining step 130 may thus include a first sub-step 131: calculating the time t between the moment when the piezoelectric actuator 51 contacts the valve 52 after sending the current pulse 110 c and the time t after the closing moment t3 of the needle 53 end The voltage change dV between them. This step is implemented based on a plurality of voltage values measured at the terminals of the piezoelectric actuator 51 of the piezoelectric injector 5. As described above, this voltage change dV characterizes the pressure change dP in the control chamber 54 cc , and the static flow rate of the piezoelectric injector 5 can be determined through this pressure change.

[0080] Optionally, in this embodiment, a second sub-step 132 can be implemented: calculating the pressure change dP in the control chamber 54 of the injector 5 cc . This calculation is performed based on the voltage change dV determined when the first sub-step 131 is completed. In fact, the voltage change dV of the piezoelectric actuator 51 corresponds to the force applied to the actuator due to the piezoelectric effect. Therefore, when the surface area of the piezoelectric actuator 51 and the force applied to it by the support of the valve 52 due to the pressure in the control chamber 54 are known, the pressure change dP in the control chamber 54 of the piezoelectric injector 5 can be calculated cc . Therefore, this gives the pressure change dP in the control chamber 54 after the needle 53 is closed.cc 。

[0081] Finally, a third sub-step 133 of determining the static flow rate of the injector 5 is performed based on a table of the voltage change dV and the static flow rate reference value of the injector.

[0082] Thus, in embodiments where the second sub-step 132 is not implemented, the reference table makes the voltage change dV directly correspond to the static flow rate of the piezoelectric injector.

[0083] In embodiments where the second sub-step 132 is implemented, the reference table makes the pressure change dP in the control chamber 54 of the piezoelectric injector 5 cc correspond to the static flow rate of the piezoelectric injector.

[0084] Whether directly through the voltage change dV of the electric actuator 51 or by using this voltage change dV to derive the pressure change dP in the control chamber 54 cc , the static flow rate of the piezoelectric injector 5 can be obtained.

[0085] Returning to Figure 3 the method shown, after completing the step 130 of determining the static flow rate of the injector 5, the method may include a supplementary step 140: generating an alarm when the absolute value of the difference between the determined static flow rate of the injector 5 and the nominal static flow rate of the injector is greater than a predetermined threshold.

[0086] In addition, the method may further include: controlling the fuel pressure in the fuel supply rail 4 according to the static flow rate determined when the determination step 130 is completed, so as to adjust the amount of fuel injected into the combustion chamber.

[0087] Advantageously, the method is only implemented when the following three conditions are met:

[0088] - When the determined duration between the closing moment t2 of the valve 52 and the closing moment t3 of the needle is greater than a predetermined threshold; and

[0089] - When the temperature of the engine is between a first predetermined temperature and a second predetermined temperature; and

[0090] - When the engine speed is between a first predetermined rotational speed and a second predetermined rotational speed.

[0091] The last two conditions make it possible to ensure that the injection system 2 operates stably enough to be able to implement the method with good accuracy and good repeatability.

[0092] Thus, the above method enables the static flow rate of a piezoelectric injector in a combustion engine to be estimated. This estimation is based on the voltage value at the terminal of the piezoelectric actuator positioned in contact with the valve of the injector. Thus, it can be implemented without modifying the existing injection system, and in particular without making it more complex. Since the method is not based on determining a predetermined closing moment of the needle, it is not affected by the transients that change the closing of the needle and are not caused by the static flow rate, in particular those related to multiple injections or to the opening of the valve controlling the piezoelectric injector. Finally, when the static flow rate of the piezoelectric injector is determined, it is possible to trigger an alarm or to control the amount of fuel injected into the engine combustion chamber by controlling the pressure of the fuel in the supply rail.

Claims

1. A method for determining the static flow rate of a piezoelectric injector (5) of an injection system (2) for a combustion engine, the piezoelectric injector (5) comprising a needle (53) and a piezoelectric actuator (51), the piezoelectric actuator being designed to control a valve (52) of the piezoelectric injector (5), the injection system (2) comprising a generator (8) and a voltage sensor, the generator being designed to send a current pulse to the piezoelectric actuator (51) of the piezoelectric injector (5), the voltage sensor being designed to measure the voltage value at the terminals of the piezoelectric actuator (51). The method is characterized in that it comprises the following steps: - sending (110) a current pulse by the generator (8) to the piezoelectric actuator (51) such that the piezoelectric actuator (51) is positioned in contact with the valve (52) without causing the valve to open, this sending being carried out during the closing phase of the needle; - measuring (120) by the voltage sensor a plurality of voltage values of the piezoelectric actuator (51); and - determining (130) the static flow rate of the piezoelectric injector (5) based on the plurality of measured voltage values of the piezoelectric actuator (51).

2. The method according to claim 1, wherein The steps for determining (130) the static flow rate include a first sub-step (131) of calculating the voltage change (dV) between the time (t c ) at which the piezoelectric actuator (51) contacts the valve (52) after the current pulse has been sent (110) and the time (t end ) after the closing time (t3) of the needle.

3. The method according to claim 2, wherein The step of determining (130) the static flow rate further includes a second sub-step (132) of calculating a pressure change (dP cc ) in the control chamber (54) of the piezoelectric injector based on a voltage change (dV) at the terminals of the electro-actuator (51).

4. The method according to claim 2 or 3, characterized in that, The step of determining (130) the static flow rate further comprises a third sub-step (133) of determining the static flow rate of the piezoelectric injector (5) based on a voltage change (dV) and a table of static flow rate reference values of the piezoelectric injector.

5. The method according to any one of claims 1 to 3, characterized in that The method is only implemented when: - a determined duration between the closing moment (t2) of the valve (52) and the closing moment (t3) of the needle is greater than a predetermined threshold; and - the temperature of the engine is between a first predetermined temperature and a second predetermined temperature; and - the engine speed is between a first predetermined rotational speed and a second predetermined rotational speed.

6. The method according to any one of claims 1 to 3, characterized in that The method comprises a supplementary step (140) of generating an alarm when the absolute value of the difference between the determined static flow rate of the piezoelectric injector (5) and the nominal static flow rate of the piezoelectric injector is greater than a predetermined threshold.

7. The method according to any one of claims 1 to 3, characterized in that, The injection system (2) further comprises a fuel supply rail (4), and wherein the fuel pressure in the fuel supply rail (4) is controlled according to the static flow rate of the piezoelectric injector (5).

8. A computer program product comprising instruction codes for implementing the steps of the method according to any one of claims 1 to 7.

9. A computer designed to control an injection system (2) for a combustion engine comprising a piezoelectric injector (5), the piezoelectric injector (5) comprising a needle (53) and a piezoelectric actuator (51), the piezoelectric actuator (51) being designed to control a valve (52) of the piezoelectric injector (5), The injection system (2) further includes: a generator (8) designed to send a current pulse to the piezoelectric actuator (51) of the piezoelectric injector (5); a voltage sensor designed to measure the voltage value at the terminals of the piezoelectric actuator (51); and a fuel supply rail (4), characterized in that the computer is further designed to control the implementation of the steps of the method according to any one of claims 1 to 7.

10. A combustion engine, comprising an injection system (2) having a piezoelectric injector (5), said piezoelectric injector (5) including a needle (53) and a piezoelectric actuator (51), said piezoelectric actuator (51) being designed to control a valve (52) of said piezoelectric injector (5), The injection system (2) further comprises: a generator (8) designed to send current pulses to said piezoelectric actuator (51) of said piezoelectric injector (5); a voltage sensor designed to measure a voltage value at terminals of said piezoelectric actuator (51); and a fuel supply rail (4), the engine being characterized in that it includes a computer as claimed in claim 9.

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