Patent Application
20060224299
The present invention has as its object a process for determining the operating parameters, also called a learning process, of an injection device of a combustion engine.
Conventionally, an injection device includes a plurality of injectors, each of the injectors being controlled to open and close by an electronic control means, by means of control signals permitting driving of one or more pilot injections and a main injection at each of the injectors. The injectors used may be of several types, for example of solenoid type or piezoelectric type.
The document EP 0 740 068 describes a solenoid injector. The injector includes an injector body. At its lower end, the injector body defines a seat in which the lower end of a needle is able to engage, the needle being able to slide between an open position in which it permits ejection of fuel from the injector and a closed position in which it sealedly closes the injector. The injector body is supplied with fuel by a high-pressure fuel source, such as a common rail, using a supply passage emerging in an annular gallery. The annular gallery surrounds the needle, in the proximity of its upper end, the form of the needle being suitable to allow circulation of fuel from the annular gallery between the bore and the needle. The high pressure supply line also communicates with a control chamber through a “restrictor”. At its upper end, the control chamber is closed by a plate. The plate co-operates with a sliding valve member including a hollow rod, the inside of the hollow rod being able to communicate with the inside of the chamber when the valve member is disengaged from the plate. The inside of the hollow rod also communicates with a low-pressure return. An electronic control means controls, by means of control signals, a solenoid actuator. When the solenoid is supplied, the valve member is disengaged from the plate. At this moment, fuel in the control chamber can escape to the inside of the hollow rod and then into the low-pressure return. When the pressure inside the control chamber drops to a certain point, the force applied to the needle due to the pressure inside the control chamber is no longer sufficient to keep the needle in its closed position. At this moment, the needle adopts its open position and fuel is ejected from the injector. When the solenoid is no longer supplied, the valve member is re-engaged in the plate under the influence of a spring. This has the effect of closing communication between the inside of the hollow rod and the control chamber. At this moment, the pressure in the control chamber increases and pushes the needle into its closed position.
The document EP 0 937 891 describes a piezoelectric injector. The injector includes a piston which defines a control chamber in combination with the upper surface of the needle. The injector includes piezoelectric actuators. The actuators are electrically connected to a control circuit able to emit control signals. The pressurised fuel present in the control chamber applies a force to the upper part of the needle and allows it to be held in the closed position, in combination with a spring. To start the injection, the piezoelectric material is discharged, in order to reduce its size. The effect of this is a movement of the piston in the direction opposite to the needle and therefore a reduction in the pressure inside the control chamber. At this moment, the needle is in its open position. When the piezoelectric material is charged, this has the effect of pushing the piston downwardly. This movement increases the fuel pressure inside the control chamber, thus increasing the force applied to the upper surface of the needle, which has the effect of pushing it back into its closed position.
Even if the injectors used in the injection device are of the same type, each injector has specific parameters. In addition, mechanical wear can also affect the accuracy of the quantity of fuel injected. Learning processes must therefore be performed to adapt the control signals to the specific characteristics of each of the injectors, in order to balance the operation of the engine to the maximum extent, to optimise combustion noise and control gas emissions. In particular, these processes permit determination for each injector of the minimum drive pulse (MDP) causing opening of the injector.
A first solution consists of using an accelerometer. However, this solution is sensitive to vibrations and this causes accuracy problems, particularly with piezoelectric injectors.
A second solution consists of using a velocity sensor permitting continuous determination of the crankshaft velocity.
The document FR 2 720 787 describes a process for determination of the specific parameters of each of the injectors of an injection device of a combustion engine, in particular of a device with pilot injection and main injection. For this purpose, the curve is determined of the difference in instantaneous velocity of the drive shaft between the instant of passage through combustion top dead centre of the cylinder in question and a subsequent predetermined instant, for example offset by 60°, prior to passage through combustion top dead centre of the following cylinder, as a function of the duration of pilot injection, the other operating parameters being kept constant. This curve presents a minimum plateau. The gradient break point of this curve permits determination of the opening time of the injector from which the injector starts to deliver. This process is intended to be implemented for example at the end of assembly line check to tune the engine or to perform tests in case of malfunction of the engine within the context of after-sales service.
The process described in this document cannot be performed when the engine is outside the idling zone, i.e. when the injectors are being controlled by control signals corresponding to a demand of a gas control organ. This process, which was designed for use during engine idling uses an instantaneous velocity difference which is very sensitive to the shape of the instantaneous velocity curve of the engine at each injection cycle. The present inventors have found that this shape lost its uniformity at high revolutions, so that the difference in question depended as much on the rotational velocity of the engine as on the quantity injected. This resulted in the impossibility of using this process quantitatively other than during idling. Moreover, the difference in instantaneous velocity which is used in this process [is] very dependent on the engine velocity, and this results in a large margin of error if the engine velocity is not constant over the whole learning period.
The present invention has the aim of proposing a process for determining the operating parameters of an injection device of a combustion engine which avoids at least certain of the above-mentioned disadvantages and which is more accurate. A further aim of the invention is to propose a learning process which can be used at different engine velocities and/or at different injector supply pressures in order to determine the relevant parameters over an extended operating range.
To this end, the invention has as its object a process for determining the operating parameters of an injection device of a combustion engine, the injection device including a plurality of fuel injectors, and an electronic control means able to control the injectors by means of injection control signals, the electronic control means being connected to a sensor permitting continuous measurement of a velocity of the combustion engine, the engine operating in accordance with an engine cycle including at least one injection cycle associated with each of the injectors, the injection cycles following each other in a predetermined order, characterised by the fact that it comprises the steps consisting of:
a) selecting an injector to test from the injectors;
b) calculating a mean velocity associated with a preceding injector arranged before the injector to test in the order of the injection cycles, which is equal to the velocity of the engine averaged over a measurement duration essentially covering one injection cycle associated with the preceding injector;
c) for the injection cycle associated with the injector to test, applying to the injector to test an injection control signal including at least one test pulse having an adjustable parameter;
d) calculating a mean velocity associated with the injector to test, which is equal to the velocity of the engine averaged over a measurement duration essentially covering the injection cycle associated with the injector to test;
e) calculating a difference between the mean velocity calculated in step d) and the mean velocity calculated in step b);
f) repeating steps b) to d) for at least another engine cycle, each time varying the parameter of the test pulse;
g) determining a value of the parameter of the test pulse for which the mean velocity difference exceeds a predetermined threshold and storing the parameter value.
In accordance with one embodiment of the invention, the injectors have direct actuation. These injectors allow a more accurate result to be obtained, due to the absence of hydraulic interaction.
Advantageously, in step c), the control signal includes a plurality of test pulses, the value of the parameter being the same for each of the test pulses.
In accordance with one characteristic of the invention, the parameter is a pulse duration.
In accordance with a particular embodiment, while the process is being performed, the injection control signals of the injectors other than the injector to be tested are nil. This corresponds for example to execution of the process when the accelerator pedal is raised.
In accordance with another embodiment, while the process is being performed, the electronic control means provides to the injectors injection control signals including a main pulse corresponding to a demand emanating from a gas control organ. This corresponds for example to execution of the process when the accelerator pedal is depressed.
Advantageously, before step g), a filtered mean velocity difference is calculated by applying a convolution by a filter to the curve representing the mean velocity difference as a function of the test pulse parameter, and the filtered mean velocity difference is used in step g). Preferably, the filter is a sliding mean.
In accordance with one characteristic of the invention, the process includes a first step consisting of testing a predetermined stability condition to detect stable operation of the engine, and a step consisting of terminating the process when the stability condition is not satisfied. Verification of the stability condition is not essential to performance of the learning process, but it simplifies data processing. The stability condition is composed of one or more elementary conditions, which my be cumulative or alternative. In particular, provision may be made for the stability condition to be verified when a plurality of elementary conditions is verified. The elementary conditions can be tested simultaneously or in succession. A non-limiting list of elementary conditions which can allow detection of a so-called stable zone is given below.
Advantageously, the stability condition includes an engine velocity condition, which condition is verified when the engine velocity is between two predetermined thresholds (minimum and maximum).
Advantageously, the stability condition includes an engine torque condition, which condition is verified when the engine torque is between two predetermined thresholds (minimum and maximum).
Advantageously, the stability condition includes a gear ratio condition, which condition is verified when the gear ratio is greater than a predetermined threshold.
Advantageously, the stability condition includes a condition of the speed of the vehicle, which condition is verified when the vehicle speed is higher than a predetermined threshold.
Advantageously, the stability condition includes a clutch engagement condition, which condition is verified when clutch engagement is activated.
In accordance with one characteristic of the invention, at each engine cycle the process includes a step consisting of calculating a difference between the mean velocity calculated in step b) for the engine cycle and the mean velocity calculated in step b) for a preceding engine cycle, a step consisting of calculating a corrected mean velocity difference by correcting the mean velocity difference calculated in step e).
In accordance with one characteristic of the invention, the velocity of the combustion engine corresponds to the rotational velocity of a crankshaft of the combustion engine, the measurement period associated with an injector extending each time between an initial instant retarded by an offset angle α of the crankshaft relative to combustion top dead centre of a piston corresponding to the injector and a final instant retarded by the offset angle α relative to top dead centre of the piston corresponding to the next injector in the order of the injection cycles. Advantageously, the offset angle α is less than or equal to 45°.
Preferably, the injection device includes a common rail provided with a high pressure valve, each of the injectors being connected to the common rail. The presence of a high pressure valve in the common rail is preferable but not essential.
In accordance with one characteristic of the invention, the process includes a step consisting of selecting a common rail pressure within a range of for example 200 to 2000 bars and performing the process while this common rail pressure is maintained in the common rail.
Advantageously, the process includes the steps consisting of detecting actuation of an organ for controlling the gases of the vehicle corresponding to a fuel demand, calculating a common rail target pressure suited to the fuel demand and, when the target pressure is lower than the selected common rail pressure, reducing the pressure in the common rail by opening the high pressure valve.
Preferably, the process includes the steps consisting of detecting actuation of an organ for controlling the gases of the vehicle corresponding to a fuel demand, calculating a common rail target pressure suited to the fuel demand and, when the target pressure is less than the selected common rail pressure, providing injection control signals to the injectors including at least one pre-injection pulse and one main pulse.
The invention will be better understood and other aims, details, characteristics and advantages of it will become more clearly apparent in the course of the following detailed explanatory description of several embodiments of the invention given as purely illustrative and non-limiting examples, with reference to the attached diagrammatic drawings. In these drawings:
With reference to
In normal operation, the drive computer 8 receives the control signal from the accelerator pedal and calculates the fuel flows having to be injected into each cylinder as a function of this signal (algorithm itself known).
The computer 8 produces injector control signals to inject the calculated flows, each time in the form of one or more pulses, for example a pilot pulse and a main pulse. These flows correspond to the quantity of fuel necessary to operation of the engine. The computer 8 calculates and adjusts the common rail pressure as a function of the fuel demand (algorithm itself known). The calculated pressure is called the common rail target pressure. For example, at 4500 rpm the pressure in the rail 6 is approximately equal to 1800 bars. The computer 8 also controls idling, which corresponds to a predetermined minimum velocity which the computer 8 maintains when no signal is transmitted by the accelerator pedal. These functionalities obtained by programming the drive computer 8 are conventional and will not be described in detail.
The computer 8 contains a learning program execution of which controls the progress of a process which will now be described.
Performance of the Process
With reference to FIGS. 2 to 4, the progress of the learning process to determine the value of a parameter of the control signal associated with an injector 7 will now be described. This process is performed while the engine is turning. The parameter which is required to be determined is, in the present case, a minimum drive pulse (MDP) of the control signal which causes effective opening of an injector 7.
In step 96, the process is initialised. This type of learning is intended to be effected during the use of the vehicle, for example initialisation takes place every quarter of an hour or every hour. By performing this process regularly, statistical processing can be carried out on the minimum duration values obtained at each execution, which allows more accurate values to be obtained.
In step 97, the rail pressure is set.
In step 98, the injector under test, i.e. the injector for which it is required to determine the minimum drive pulse, is selected. In
In step 99, an initial drive pulse D0 is set. The initial drive pulse D0 corresponds to the duration of a test pulse which will be sent to the selected injector to perform injection cycle 22, for example in the vicinity of top dead centre 33 of the engine cycle, during the first passage through loop 43 of the process. A drive pulse D is then incremented on each passage through loop 43, a test pulse of a duration equal to the current drive pulse in loop 43 being sent to the injector selected to perform injection cycle 22, for example in the vicinity of TDC 33, at each engine cycle during the process. The expression each engine cycle in fact designates the cycles during which the loop 43 is executed. Two successive passages through loop 43 can optionally be spaced apart one from the other.
Steps 100 to 106 will now be described, on a passage through loop 43. The number of passages through the loop 43 is indexed by an index in the following description. For illustration, three successive passages are referred to below, of rank n−1, n and n+1.
In step 100, a stability condition, which will be described in detail below with reference to
Step 101 consists of calculating a mean velocity ω21,n−1 (
ω21,n−=1/T.∫ (1)
The initial instant t1 of the measurement period T is for example offset relative to top dead centre 31 by a period 32 which corresponds to an angle of offset α of rotation of the crankshaft. In this case, the final instant t2 of the measurement period T is offset by the same angle α relative to top dead centre 33 associated with the next injector.
The step 102 consists of calculating a mean velocity ω22,n−1 of the engine over injection cycle 22. The mean velocity ω22,n−1 is calculated over a duration T′ which is offset from TDC 33 by the angle of offset α. This angle of offset α permits expectation that the test pulse sent to the selected injector, which occurs in the vicinity of top dead centre 33, has had its effect, i.e. causing an effective injection of fuel in the injection cycle 22, where necessary, and therefore combustion. This angle of offset α is for example of the order of 30°. The test pulse of current duration Dn−1, which has been generated in the vicinity of TDC 33, is shown by way of illustration on the first line of
When the mean velocity ω22,n−1 has been calculated, the process passes to step 103, which consists of calculating the mean velocity difference
ΔΩn−1=ω22,n−1−ω21,n−1.
It will be noted that calculation of the mean velocity difference over two consecutive injection cycles 21, 22 allows limitation of the influence of external parameters on the mean velocity difference. In particular, the variation in mean velocity due to natural slowing of the engine is negligible over such a short duration. The pair (ΔΩn−1,Dn−1) is stored. Step 103 can also be performed outside loop 43.
In step 104, a pulse duration Dn greater than the duration Dn−1 is selected. The pulse of duration Dn is shown by way of illustration on the second line of
In step 105, the duration Dn is compared with a pre-selected maximum pulse duration Dmaxd. If the duration Dn is less than the maximum duration, the process returns to step 100 for another passage through loop 43, otherwise passage is made to step 106. In the present case, it is considered that the duration Dn is less than the duration Dmax.
At the next passage through loop 43, the mean velocities ω21,n and ω22,n are calculated in similar manner.
At the next passage through loop 43, the mean velocities ω21,n+1 and ω22,n+1 are calculated in a similar manner.
Loop 43 is repeated in similar manner until the pulse duration reaches the maximum duration Dmax or the stability condition is no longer verified.
When the process quits loop 43, it passes to step 106.
In step 106, the stored mean velocity differences ΔΩn−1, ΔΩn, ΔΩn+1 are filtered by convolution with a lowpass filter W, so as to smooth differences due to noise, in particular to measurement uncertainties. The filter W is for example a sliding mean centred using values preceding and values following the value to be verified, for example with weighting in the form of a sinusoidal or Gaussian arc.
ΔΩf==ΔΩ(D)*W=∫ΔΩ(D−D′).W(D′)dD′.
In practice, the convolution is calculated discretely. For the sake of clarity,
Step 107 consists of determining the drive pulse MDP from which it is considered that an injection has actually occurred. For this purpose, the values of the curve 57 are compared with a predetermined threshold 58. The threshold 58 is so selected that it is located above the noise.
It will be noted that the minimum drive pulse MDP0 is initially known for each injector 7, subject to a tolerance range, for this is a specification of the new injector. The existence of a small error in the initial value is not a problem, as the process finally permits its correction. The minimum drive pulse MDP changes when the injector 7 ages. To find the minimum drive pulse MDP, one solution therefore consists of scanning the curve 57 in the direction of increasing drive pulse durations D over an interval centred on the known preceding minimum drive pulse MDP0. For example, the scanned interval may extend from 100 μs to some hundreds of μs. D0 and Dmax are for example set such that D0=MDP0−50 μs and Dmax=MDP0+50 μs, the minimum drive pulse MDP0 being of the order of 100 μs. Another solution consists of scanning this interval by dichotomy.
In step 108, the value of MDP is stored. When the value of MDP has been stored, the process may return to step 98, if the minimum drive pulse of another injector is to be determined, to step 97 if the minimum drive pulse of an injector is to be determined for a different rail pressure, or to step 96 if the learning process is terminated. In this case, the process awaits an initialisation signal to re-start.
Determination of a Stable Zone
In step 80, the first test, Test 1, consists of verifying that the accelerator pedal is completely released.
In step 81, the second test, Test 2, consists of verifying that the engine velocity is within an acceptable range. This range is for example between 750 and 3000 rpm. Outside this, a test pulse creates very little variation in the engine velocity ω, even if there is actually an injection, due to the inertia of the engine. Moreover, the crankshaft sensor 12 having a measurement period of the order of the microsecond, increasing the crankshaft velocity increases the margin of error.
In step 82, the third test, Test 3, consists of verifying that the gear-box is in the correct range. This corresponds for example to a gear ratio between third and fifth. In fact, in first or second, acceleration or braking causes abrupt variations in engine velocity and this causes problems in measurement accuracy. This test comes down more or less to verifying that the speed of the vehicle is greater than 30 km/h, which condition could also be the subject of a test.
In step 83, the fourth test, Test 4, consists of verifying that clutch engagement is activated, i.e. that the engine is coupled to the wheels. At 2500 rpm, when the user declutches, the velocity drops very quickly, which poses correction problems, as will be described later in detail.
In step 84, the fifth test, Test 5, consists of verifying that the temperatures of the water, fuel, air and oil are within an acceptable range. At very low temperature, combustion is unstable. When the engine is hot, friction is minimised. This test therefore serves to anticipate that the engine will be in steady state.
To these tests can be added other tests intended to verify the correct operation of the equipment required by the process.
Here, in step 85, the sixth test, Test 6, consists of verifying that the voltage at the battery terminals is correct.
In step 86, the seventh test, Test 7, consists of verifying that no sensor 12 essential to the proper operation of the process is malfunctioning.
The stability condition is verified when all the tests are verified. For example, a logic variable S may be used. In this case, the stability variable S is set to 1 in step 79. If one of the above-mentioned tests produces a negative result, the variable S is set to 0 in step 78. The value of this variable is used in step 100 to determine whether loop 43 must be performed.
Stopping the Process
The value of the minimum drive pulse MDP depends on the pressure of the common rail 6. This MDP value varies when the pressure of the common rail 6 varies. It is therefore desirable to perform the learning process for pressures of rail 6 covering the widest possible pressure range. The stability condition defined in
For this purpose, a high pressure valve 10 is opened to lower the pressure in the common rail 6 when this is to be decreased. The high pressure valve 10 permits very rapid reduction of the pressure in the rail 6. For example, a high pressure valve permits a reduction of the order of 2000 bars/s. The use of a high pressure valve 10 therefore permits very rapid reduction of the rail pressure after learning at high pressure.
In addition, it is advantageous for the drive computer 8 to control the injectors with at least one pilot pulse before the main pulse, so as to produce an additional pilot injection very close to the main injection, which also permits reduction of combustion noise. The additional pilot injection is so positioned as to reduce the noise to the maximum extent, for example as close as possible to the main injection.
As indicated, the process described above functions correctly over a wide operating range of the engine, for example from idling to 3000 rpm. As a velocity averaged over an injection cycle is used to determine the MDP parameter, the process is not sensitive to the precise shape of the arch corresponding to each injection cycle. Even at high revolutions, when the arches start to be deformed by inertia of the engine, the process always produces reliable results.
The learning process, described above in the case of operation with the foot raised, can also be performed during operation in a stabilised state, when the accelerator pedal is pressed in a substantially constant manner, and the fuel flows calculated by the drive computer 8 are therefore stable and identical for all the injectors. In this modified embodiment, Test 1 is replaced by a Test 1′ which tends to test whether these conditions are verified. The process is otherwise identical. In this case, all the injectors receive control signals from the drive computer 8, for example in the form of a main pulse preceded by one of more pilot injections. These pulses are fixed relative to the top dead centres of the pistons in accordance with a known technique. The injector under test in addition receives the test pulse or pulses, which can for example be positioned in advance of the main pulse or, where necessary, the pilot pulse.
The necessity of providing for the supplies to all the injectors can impose limits on the range within which the rail pressure can be fixed during learning. In fact, it is necessary to prevent excessive combustion noise. For this purpose, it is preferable to perform injection into the cylinders in the form of multiple pulses. The presence of one or more pilot injections prepares and heats the mixture of diesel oil and air and tends to reduce noise by lengthening the duration of combustion.
A second embodiment will now be described in which the process can be performed in a so-called unstable zone, i.e. in which, in addition to the fact that the cylinders are allowed to be supplied with fuel, the engine velocity is allowed to vary relatively rapidly. Correction calculations permit compensation for the variations in engine velocity due to the influence of parameters external to the learning process, such as acceleration or braking. With reference here to
In this embodiment, the stability condition to be tested can be rendered much less restrictive (step 200). Of course, steps 81 to 86 of
The description of two passages through loop 143 will be sufficient to understand its principle. Step 201 consists of storing the instantaneous engine velocity ω over a duration T essentially covering injection cycle 21, which immediately precedes cycle 22. The duration of acquisition T is identical to the first embodiment. This batch of measurements is called v21,n.
Step 202 consists of storing the instantaneous engine velocity ω over a duration T1 essentially covering injection cycle 22. This batch of measurements is called v22,n. The set (v21,n, v22,n, Dn+1) is stored.
Step 204 is identical to step 104.
Step 205 is identical to step 105. In the present case, it is considered that the duration Dn+1 is less than the duration Dmax. At the next passage through loop 143, the velocities v21,n+1 and v22,n+1 are stored in similar manner. The set (v21,n+1, v22,n+1, Dn+1) is stored.
In this embodiment, loop 143 only includes steps of acquisition of the instantaneous engine velocities over injection cycles 21 and 22. When the process quits loop 143, it passes to step 203.
In step 203, the mean engine velocity ω21,n, over injection cycle 21 is calculated from the instantaneous velocity v21,n, in a manner which has been described in detail in the first embodiment, and the mean engine velocity ω22,n over injection cycle 22 is calculated from the instantaneous velocity v22,n. The mean velocity difference ΔΩn+1=ω22,n+1−ω21,n+1 is calculated. The pair (ΔΩn, Dn) is stored. In a similar manner, the mean engine velocity ω21,n+1 over injection cycle 21 is calculated from the instantaneous velocity v21,n+1, the mean engine velocity ω22,n+1 over injection cycle 22 is calculated from the instantaneous velocity v22,n+1, and then the mean velocity difference ΔΩn+1=ω22,n+1−ω21,n+1 is calculated. The pair (ΔΩn+1, Dn+1) is stored.
In step 201A, the mean velocity ω21,n is compared with the mean velocity ω21,n−1 and an offset κn is calculated from the difference ω21,n−ω21,n−1. In the same manner, an offset κn+1 is calculated from the difference ω21,n+1−ω21,n.
In step 203A, the offset κn (κn+1 respectively) is used to calculate a correctional factor f(κn) (f(κn+1) respectively) which is subtracted from the velocity difference ΔΩn (ΔΩn+1 respectively), so as to store a corrected mean velocity difference ΔΩc=ΔΩn-f(κn) (respectively). This correctional factor compensates for the engine velocity variations due to braking and acceleration.
In step 206, the stored corrected mean velocity differences ΔΩcn, ΔΩcn+1 are filtered by convolution with the lowpass filter W.
An example of the result obtained with this process is shown in
The curves 60 and 61 shown in
When the engine ages, the compression rates of the different cylinders can be modified, which causes different engine velocities over the different injection cycles. This results in unbalancing of the engine. The object of step 209 is to measure the influence of this type of imbalance on the mean velocities ω21,n and ω22,n and to correct the mean velocity difference ΔΩn to compensate for this influence. For this purpose, the value of the mean velocity difference ω21,i−ω22,i is used in the absence of a test pulse. This value can be determined before execution of the learning process or during it, for example in the course of a passage i through loop 143 during which the test pulse is suppressed. A correctional factor is therefore calculated from the mean velocity difference ω21,i−ω22,i and applied [to] the mean velocity difference ΔΩn or ΔΩcn.
In step 210, the mean engine velocity Ωn over the engine cycle corresponding to the loop of rank n at which the process is being performed is taken into account. Due to the inertia of the engine, the mean velocity difference ΔΩn generated by a given test pulse depends on the engine velocity. For example, when 1 mg of fuel is injected at 1000 rpm, the deviation in the mean velocity ΔΩn generated is greater than that produced by an injection of 1 mg at 3000 rpm. The mean velocity differences ΔΩn obtained are then adjusted by a scaling factor dependent on Ωn. This scaling factor is for example calculated prior to the execution of the process and stored in the drive computer 8. For this purpose a curve ΔΩ as a function of Ω can be traced over a wide range of velocities Ω for a test pulse corresponding to a predetermined injected quantity and the gradient of this curve used as the scaling factor. This adjustment step allows accurate results to be obtained without having to modify the value of the detection threshold 58. Another solution would be to adapt the threshold 58 is similar manner.
Step 207 consists of determining the minimum drive pulse MDP from which it is considered that an injection has actually taken place. For this purpose, the values of the curve 60 are compared with the predetermined threshold 58.
Step 208 is identical to step 108.
Steps 203A, 209 and 210 are correctional steps which are optional. Each of these steps is intended to compensate for a particular phenomenon and can therefore be employed separately from the others or in combination. These correctional steps can also be applied in the first embodiment.
The processes described above can be performed with all types of injector. However, injectors with direct activation allow better accuracy to be obtained, in particular when multiple injections have to be performed.
In the case of use of a solenoid injector, opening is effected in two stages. In a first stage, the valve member is disengaged from the plate, and then in a second stage the needle lifts. Opening of the valve member occurs approximately 150 μs before the opening of the needle. This opening in two stages is explained in particular by the fact that the power generated by the solenoid is not sufficient to lift the needle directly. For certain pilot pulse durations, it may therefore happen that the valve member is disengaged but the needle does not lift. In this case, a flow of fuel is created from the control chamber to the low pressure return. This has the effect of creating pressure waves. In particular, in the case of a multiple injection, the main injection is interfered with by the wave created by the pilot injection and this interference depends on the separation δ. This phenomenon is illustrated in
This problem does not occur with injectors with direct actuation, such as piezoelectric injectors 73. The learning process described in the present invention is therefore particularly suited to injectors with direct actuation, for example piezoelectric injectors 73, although it can also be implemented with solenoid injectors 72, taking into account the behavioural difference.
Other modifications are also possible. For example, in each embodiment, the control signal can include a plurality of test pulses of the same duration D. For example, a test pulse is so positioned that the crankshaft is situated before TDC and a second test pulse is so positioned that the crankshaft is situated close to TDC. The mean velocity difference ΔΩ being proportional to the difference in the quantity of fuel injected by the injectors associated with the two cycles 21, 22, this difference is thus multiplied by the number of pulses, which permits improvement of the detection accuracy by increasing the gradient of the curve in
It will be noted that it is also possible to calculate the means velocity over another injection cycle preceding cycle 22, for example cycle 20.
It will be noted that the higher the revolutions, the more frequent are the injections. At 2000 rpm, injection occurs every 60 ms and it takes approximately 2 s to perform learning. When the number of revolutions per minute increases, the learning time decreases.
Certain steps of the learning process can be performed in a different order or simultaneously without changing the result.
In addition, the learning processes described can be immediately adapted to determining any other parameter of the control signal. For this purpose, the test pulse can be modified by a parameter other than its duration, for example gradient, amplitude, or other parameter.
Although the invention has been described in relation to several particular embodiments, it is quite obvious that it is in no way limited to them and that it includes all the technical equivalents of the means described and their combinations if these fall within the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 05290675.7 | Mar 2005 | EP | regional |
