Patent Grant
8210155
The present invention relates to a pressure control method and a pressure control device in an accumulation chamber (a common rail) adapted for use in constituting an accumulator fuel injection apparatus employed for a diesel engine and the like.
An accumulator (a common rail type) fuel injection apparatus is constructed to implement pumping of fuel under a pressure to a common accumulation chamber by means of a high pressure fuel feed pump driven by an engine and to allow a fuel injection nozzle of each cylinder to be connected to the accumulation chamber, so as to inject the high pressure fuel stored in the accumulation chamber to each cylinder of an internal combustion engine.
The fuel injection amount to each cylinder is uniquely determined by a pressure prevailing in the accumulation chamber, i.e., an accumulation chamber pressure, and an electric conduction time for which electricity to the fuel injection nozzles (injectors) provided for the respective cylinders lasts.
Accordingly, accurate control of the accumulation chamber pressure enables to achieve highly precise fuel injection control.
In general, fuel pumping control from a fuel feed pump to an accumulation chamber often has, as shown in
Then, an output of the feedback control unit 01 and an output of the feedforward control unit 02 are added together and a pump discharge command value, for example an amount of plunger stroke as a pump discharge command value when a pump 03 is comprised of a plunger pump, is commanded to drive the pump 03 so as to feed the fuel to a common rail 04, and thus the pressure in the common rail 04 is controlled so as to be maintained at determined target pressure.
The maps used in the above-mentioned feedforward control unit 02 are often obtained by experiment in advance. Another technique also may be applied to obtain a feedforward amount from inverse characteristics of a formulation model of pump and common rail.
For example, techniques disclosed in Patent Document 1 (Japanese Laid-Open Patent Application No. 2005-76618) and Patent Document 2 (Japanese Laid-Open Patent Application No. 2005-301764) are known regarding pressure control in a common rail.
In this Patent Document 1, a technique of using both feedforward control and feedback control is disclosed, in which pressure in the common rail is equalized by repeating a procedure of, in correspondence with the crank angle of an engine, detecting fuel pressure in the common rail to calculate a difference from predetermined target fuel pressure, outputting a part of the pressure difference as a feedforward amount, applying feedback control to the rest, and adding the feedforward amount to an output of the feedback.
In addition, Patent Document 2 creates a dynamic model for a common rail system and calculates a control amount in association with a target fuel pressure based on the model to thereby execute the feedforward control.
Nevertheless, since a feedforward amount is determined by a combination of a target pressure, a command value of fuel injection amount, and a number of engine revolutions in the feedforward control unit 02 shown in
In addition, although the technique of Patent Document 1 complements a response delay of feedback control complemented with feedforward control using both the feedforward control unit 02 and the feedback control unit 01, such control is insufficient in a case that any unexpected disturbance is developed, and furthermore, the technique disclosed in Patent Document 2 does not exhibit sufficient control performance when a disturbance other than the conditions for creating the dynamic model of common rail system is developed.
The present invention was, therefore, made in light of the described background, and the problem to be solved by the invention is to provide a pressure control method and a pressure control device that do not deteriorate control performance of accumulation chamber pressure even in the presence of any disturbance by estimating a disturbance pressure acting on an accumulation chamber (a common rail) which constitutes an accumulator fuel injection apparatus applied to a diesel engine and the like with observer control, and by correcting a pump discharge command with a compensation value compensating for the estimated disturbance pressure.
In order to solve the above-described problems, a first aspect of the present invention provides a method of controlling an accumulation chamber pressure in an accumulator fuel injection apparatus, which includes an accumulation chamber for storing fuel under pressure, a fuel injection nozzle for injecting the fuel in the accumulation chamber into an internal combustion engine, and a fuel pump for pumping the fuel under pressure to the accumulation chamber, an accumulator fuel injection apparatus controlling a pump discharge amount of the fuel pump to bring a fuel pressure prevailing in the accumulation chamber to a target pressure, wherein the method comprises the steps of: calculating a pump discharge command value of the fuel pump by using feedback, based on a pressure difference between an actual accumulation chamber pressure detected by a fuel pressure sensor and the target pressure of the accumulation chamber; producing a numerical model of the pump discharge command value of the fuel pump, a disturbance pressure acting on the accumulation chamber, and an accumulation chamber pressure by using a transfer function of the fuel pump; estimating a pressure of the disturbance from the numerical model; deriving a compensation value to compensate for the disturbance by using a disturbance observer; and correcting an output calculated by the feedback with the disturbance compensation value derived by the disturbance observer.
In addition, a second aspect of the present invention provides a device for controlling accumulation chamber pressure in an accumulator fuel injection apparatus including: an accumulation chamber for storing a pressurized fuel; a fuel injection nozzle for injecting the fuel in the accumulation chamber into an internal combustion engine; a fuel pump for pumping the fuel under pressure to the accumulation chamber; and control means for controlling a pump discharge amount of the fuel pump so as to bring a fuel pressure prevailing in the accumulation chamber to a target pressure, wherein the control means comprises: a feedback control unit configured to calculate a pump discharge command value of the fuel pump by using feedback, based on a pressure difference between an actual accumulation chamber pressure detected by a fuel pressure sensor and a target pressure in the accumulation chamber; and a disturbance observer control unit configured to generate a numerical model of the pump discharge command value of the fuel pump, a disturbance pressure acting on the accumulation chamber, and an accumulation chamber pressure by using a transfer function of the fuel pump, to estimate a disturbance pressure from the numerical model, and to derive a compensation value capable of compensating for the disturbance, and wherein an output from the feedback control unit is corrected with a disturbance compensation value from the disturbance observer control unit.
In accordance with the controlling method of the first aspect of the present invention and the controlling device of the second aspect of the present invention, application of the disturbance observer controlling enables to produce the numerical model of the discharge command value of the fuel pump, the disturbance pressure acting on the accumulation chamber, and the accumulation chamber pressure by using the transfer function of the fuel pump, to estimate the disturbance pressure from the numerical model, and to derive the compensation value that is capable of compensating the disturbance to thereby correct the output value of the feedback controlling with the compensation value. Therefore, compensation performance against the disturbance is more improved than the prior art in which the control is conducted by using the feedback control together with the feedforward control.
That is to say, since the disturbance per se is derived from the numerical model for estimation, control accuracy against the disturbance is more improved in comparison with a conventional case where the disturbance is preliminarily set in a map as conditions.
Further, a lot of time and labor to be used for creating multidimensional maps by adding disturbance conditions are not needed and thus, the controlling of the pressure prevailing in the accumulation chamber can be achieved by extremely simple means.
Moreover, in the first aspect of the present invention, the internal combustion engine is preferably comprised of a diesel engine, and an output from the feedforward control unit that calculates the pump discharge command value preliminarily set, based on the target pressure, the number of engine revolutions, and the command value of fuel injection amount is preferably added further to the feedback output. In addition, in the second aspect of the present invention, it is preferred that an internal combustion engine is comprised of a diesel engine, and the device further comprises a feedforward control unit that calculates a pump discharge command value preliminarily set, based on the target pressure, the number of engine revolutions, and the command value of fuel injection amount, and an output from the feedforward control unit is preferably added to the feedback output.
In accordance with the configuration of the control method of the first aspect of the present invention and the control device of the second aspect of the present invention, since a high responsivity in the feedforward control is added, a high responsivity due to the feedforward control is ensured and in addition, because of the fact that the disturbance compensation is effected by the disturbance observer control, the control performance is furthermore improved.
Moreover, in the first aspect of the present invention, the disturbance observer preferably blocks an output of the disturbance compensation value if the derived disturbance compensation value exceeds a given chosen range, and in the second aspect of the present invention, the disturbance observer control unit preferably includes a limiter capable of blocking an output of the disturbance compensation value if the derived disturbance compensation value exceeds a given range.
In accordance with such configurations of the first and second aspects of the present invention, when the disturbance compensation value exceeds a given chosen range, blocking of the output of the disturbance compensation value is performed so as to prohibit the disturbance observer control to be executed, whereby control is carried out only with either only the feedback control or both the feedback control and the feedforward control.
Thus, it will be understood from the foregoing that since the accumulation chamber and the fuel pump can be protected by providing the output of the disturbance observer with such a limitation that divergence of the observer control output may be avoided even if any extraordinarily large disturbance is developed, reliability of compensation function exhibited by the disturbance observer control is improved.
It should here be noted that blocking of the output, in a case that an output of the disturbance observer exceeding the limitation lasts for a certain period of time in sequence, can prevent occurrence of stopping of the control due to any transient disturbance.
In accordance with the present invention, it is possible to provide a method of and a device for controlling a pressure in an accumulation pressure chamber that constitutes an accumulator fuel injection apparatus applied to a diesel engine and the like, which method and device estimate, with observer control, a disturbance pressure that acts on the accumulation chamber (common rail) constituting the accumulator fuel injection apparatus, and correct a pump discharge command with a compensation value compensating for the estimated disturbance pressure and therefore, control performance in the controlling of accumulation chamber pressure cannot be deteriorated even in the presence of the disturbance.
Preferred embodiments of the present invention will now be described more in detail by exemplification with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, forms, relative positions and so forth of the constituent parts and elements in the embodiments will be interpreted as illustrative only not as limitative of the scope of the present invention.
(First Embodiment)
The first embodiment of the present invention is described with reference to
Further, the fuel is fed to the high pressure fuel pump 11 from a fuel tank 23 via a fuel feed pump 15, a relief valve 17, a check valve 19, and a fuel feed pipe 21, and the high pressure fuel is fed to the common rail 5 from the high pressure fuel pump 11, via a check valve 25, and a communicating pipe 26.
When the fuel feed pump 15 feeds the fuel under a pressure higher than a determined pressure, the relief valve 17 releases a part of the fuel pressure by releasing the fuel from the fuel feed pipe 21 to the fuel tank 23. In addition, while a plunger 27 of the high pressure fuel pump 11 rises, the check valve 19 blocks the fuel feed pipe 21 to prevent a backflow. The check valve 25 also prevents high pressure fuel from flowing back from the accumulation chamber 5 to the high pressure fuel pump 11.
The high pressure fuel pump 11 is shown, for example, in the form of a plunger type. The fuel is pressurized by vertical reciprocation of the plunger 27, in a plunger chamber 29, by a cam 31 driven by the diesel engine 3. Then, by controlling an effective stroke of the plunger 27, such as modifying the cam profile, with signals from the control means 13 described later, the fuel discharge amount fed to the common rail 5 is controlled, and thus the fuel pressure in the common rail 5 is controlled at a constant pressure.
The high pressure fuel from the common rail 5 is fed to the fuel injection nozzles 7 of each cylinder via feed pipelines 33, and is controlled in injection timing and injection amount of fuel to each cylinder by controlling opening and closing of electromagnetic valves 35 provided with the fuel injection nozzles 7 of each cylinder. In addition, from the fuel injection nozzles 7, the fuel left uninjected is returned to the fuel tank 23 through a fuel return pipe 37.
In the accumulator fuel injection apparatus 1 constituted as described above, the control means 13 is provided with a feedforward control unit 40, a feedback control unit 42, and a disturbance observer control unit 44.
Then, a signal from a fuel pressure sensor 46 detecting an actual pressure of the common rail 5 is inputted to the control means 13 and thus, the actual pressure, a number of engine revolutions, a command value of a target fuel injection amount (engine load) are inputted, respectively.
In the feedback control unit 42, an amount of feedback control is calculated by PID control based on a pressure difference between target pressure of the common rail 5 predetermined by the operational conditions of the engine (number of revolutions, loads) and an actual pressure of the common rail 5 detected by the fuel pressure sensor 46, and thus a pump discharge command value is calculated.
In addition, in the disturbance observer control unit 44, a formulation model of the system shown in
The system of
PR=G(s)AP+PD (1)
PR: Pressure of Common Rail
PD: Disturbance Pressure
AP: Pump Effective Stroke
Accordingly, disturbance pressure PD can be estimated by Expression (2), below.
PD=PR−G(s)AP (2)
To estimate the disturbance pressure, the pump effective stroke and the pressure of the common rail have to be detected. Although the pressure of the common rail is detectable with the sensor, the pump effective stroke is difficult to be detected, and therefore, given is pump effective stroke AP≈command value of pump effective stroke AR, a disturbance pressure estimated value {circumflex over (P)}D is derived by Expression (3).
{circumflex over (P)}D=PR−G(s)AR (3)
The disturbance pressure can be compensated for by changing the pump effective stroke. Accordingly, the disturbance pressure estimated value is converted into a pump effective stroke compensation value AH.
The conversion is carried out by utilizing an inverse function GP−1(s) of a linear pump transfer function GP(s) as Expression (4).
AH=GP−1(s){circumflex over (P)}D=GP−1(s)PR−AR (4)
If there is a differential term in the inverse function GP−1(s), a noise signal in a common rail pressure signal is also differentiated to eventually cause any vibration in the common rail. Observer bandwidth ωD is thus introduced, and the result of executing the filtering equation is represented as Expression (5).
Based on the pump effective stroke compensation value A′ processed with a bandwidth derived as above, an output from the feedback control unit 42 (
As shown in the block diagram of control logic in
In this disturbance observer control unit 44, actual common rail pressure PR, including disturbance pressure acting on the common rail 5, that is pressure fluctuation within the common rail 5 due to fuel injection from the fuel injection nozzles 7 to respective cylinders, pressure fluctuation based on mechanical vibrations due to injection by the fuel injection nozzles 7, etc., is inputted from the fuel pressure sensor 46.
Then, an inverse function unit 52 of a pump transfer function is multiplied, and the command value AR of pump effective stroke is subtracted from the result in an adder/subtractor 54, and then a filtering unit 56 of a vibration frequency bandwidth of the bandwidth ωD is multiplied with the result to obtain the pump effective stroke compensation value A′ based on Expression (5) in which the high frequency components for noise is removed.
Then, the output from the feedback control unit 42 is corrected in the subtractor 50, and the command value of pump effective stroke after correction is inputted to the transfer characteristics unit 58 of the pump and common rail system.
In practice, the discharge amount is controlled by a command indicating the plunger stroke of the high pressure fuel pump 11.
According to the first embodiment described above, by estimating disturbance pressure in the disturbance observer control unit 44 from a command value of pump effective stroke and actual common rail pressure and by deriving a pump effective stroke compensation value that compensates the disturbance pressure to zero, the output from the feedback control unit 42 is corrected to calculate the command value of pump effective stroke, so that the compensation performance against disturbance is more improved than the control using both feedback control and feedforward control according to the prior art.
In other words, since a disturbance per se is derived from a numerical model for estimation, control accuracy for the disturbance is more improved in comparison with a case where a disturbance is preliminarily set in a map as one of conditions.
Further, a lot of time and a lot of labor and efforts that are needed for creating multidimensional maps by adding disturbance conditions are not required, and the pressure in the accumulation chamber can be controlled by the extremely simple means.
(Second Embodiment)
Next, with reference to
In the second embodiment, a feedforward control unit 40 is further added to the first embodiment. Target common rail pressure is set that is predetermined by engine operational conditions, which are a number of engine revolutions and a command value of target fuel injection amount (engine load), inputted to the control means 13, and a command value of a pump effective stroke pre-mapped based on the experiments conducted is preliminarily calculated in this feedforward control unit 40, based on the number of engine revolutions, the command value of target fuel injection amount, and a target accumulation chamber pressure.
Then, the command value of the pump effective stroke calculated in this feedforward control unit 40 is added to a command value from the feedback control unit 42 in an adder/subtractor 60, and the pump effective stroke compensation value A′ derived in the disturbance observer control unit 44 as described in the first embodiment is subtracted for correction, and thus a command value of the pump effective stroke is calculated.
Accordingly, a high responsivity due to the feedforward control unit 40 is secured by adding the high responsivity of the feedforward control unit 40, and an entire control performance is furthermore improved by the disturbance compensation executed by the disturbance observer control unit 44.
(Third Embodiment)
Next, with reference to
In the third embodiment, a limiter 65 is provided to the first embodiment in a disturbance observer control unit 67 to avoid any divergence of the disturbance observer control. The other construction and arrangement are similar to the first embodiment.
As shown in
Since the common rail 5 and the high pressure fuel pump 11 can be protected by providing such limitation for the disturbance observer output and avoiding the divergence of the observer control output when extraordinarily large disturbance is developed, reliability of the pump effective stroke compensation value A′ by the disturbance observer control unit 44 is improved.
It should be noted that blocking the output, in a case that an output exceeding the limitation is continued for a certain period of time in sequence, can prevent stopping control due to the transiently developed disturbance, and thus the reliability of the disturbance observer control unit 44 can be even further improved.
(Fourth Embodiment)
Next, with reference to
The fourth embodiment has a configuration such that both the described second and third embodiments are incorporated therein, and as shown in
According to such fourth embodiment, high responsivity due to the feedforward control unit 40 is secured, and the operational reliability of the disturbance observer control unit 44 is improved by including the limiter 65, and thus, both reliability and control performance for the disturbance pressure are more improved.
Industrial Applicability
According to the present invention, since deterioration in control performance of accumulation chamber pressure can be prevented even in the presence of any disturbance by estimating a disturbance pressure, with observer control, acting on the accumulation chamber (common rail) constituting the accumulator fuel injection apparatus applied to a diesel engine and the like, and by correcting the pump discharge command with a compensation value compensating the estimated disturbance pressure, the present invention is useful for application to a method of controlling accumulation chamber pressure of accumulator fuel injection apparatus, such as a diesel engine and the like, and a pressure control device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-009549 | Jan 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/068812 | 10/9/2008 | WO | 00 | 12/8/2009 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/090782 | 7/23/2009 | WO | A |
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