FI125058B - Control system and control method for internal combustion engine, and internal combustion engine - Google Patents

Description

Control system and control method for an internal combustion engine, and an internal combustion engine

TECHNICAL FIELD

The invention concerns in general technology of internal combustion engines such as large diesel engines. In particular, the invention concerns the way in which the feedback control is utilized to control the values of the dynamic quantities in the internal combustion engine during its operation.

BACKGROUND OF THE INVENTION

Operating a modern internal combustion engine, such as a large diesel engine, involves setting up and running a number of feedback control loops to control the corresponding processes that take place as part of the operation of the engine. Fig. 1 is a schematic illustration of a process 101 and a controller 102 that apply feedback control. The sensor 103 monitors the state of the process 101 and produces a feedback value which is an indicator of a measured dynamic quantity such as e.g. pressure, temperature, speed, frequency, flow rate, surface level, or the like. The controller 102 Compares the feedback value to a setpoint value and produces an output on the basis of the comparison. The output results in a control signal to an actuator 104, with the aim of changing the state of the process 101 so that the difference between the feedback value and the setpoint value would become as small as possible. Known feedback control schemes may include, for example, proportional control, integral control, and / or derivative control. In these, the intensity of the corrective action depends on the current difference to setpoint (proportional), the weighted sum of the current and previous differences (integral), or the slope of the difference over time (derivative).

Disturbances are the factors that tend to change the state of the process 101. Measurable disturbances are those the effects of which are known beforehand and / or can be measured online with reasonable accuracy. Additionally, there are non-measurable disturbances that may involve e.g. the mechanical wear of components in the process 101. The effect of non-measurable disturbances on the state of the process 101 are difficult, if not impossible, to predict.

Pure closed-loop feedback control such as in FIG. 1 involves the inherent disadvantage that it only reacts to the effects that it has already taken place in the process, and thus involves certain latency and dynamics. Figure 2 illustrates how this disadvantage can be at least partially dealt with by adding an element of feed-forward control. The control system shown in fig. 2 comprising, in addition to the elements explained above, in association with fig. 1, a feed-forward controller 201. It is configured to receive one or more input values that are indicative of currently measurable disturbances. The feed forward controller 201 produces an output that is at least partially based on its input value (s). The outputs of both the feedback controller 102 and the feed forward controller 201 are coupled to a combiner 202 which delivers their combination as a control signal to the actuator 104. The combination is not necessarily a straightforward sum, but it is intuitive to think. that way in which the actuator 104 should affect the state of the process 101 takes into account the outputs of both controllers.

As an example we may think that process 101 is a common rail fuel injection, and sensor 103 monitors the pressure in the fuel delivery line delivering fuel to the injectors for injection into the cylinders of the internal combustion engine. In this example, the actuator 104 drives the flow control valve, which controls the fuel flow into the fuel delivery line (i.e., the rail). Deliberate increase in injection duration is a measurable disturbance. If only feedback control was applied according to fig. 1, the increased injection duration would cause a pressure drop. The sensor 103 would convey the decreasing pressure values to the feedback controller 102, which would then try to compensate the measured pressure drop by using the actuator 104 to open more the flow control valve. Latency and Dynamics in the feedback control loop would mean that a certain transient drop in the common rail pressure was inevitable.

If the control system of FIG. 2 was in use, the feed forward controller 201 would receive information about the increase in injection duration in real time. The feed forward controller 201 can then react quickly by producing an output signal which, after going through the combiner 202, increases the fuel flow to the rail faster than in the simple feedback control case explained above.

The weakness of the combined control approach of FIG. 2 is that the feedforward controller 201 inevitably operates on the basis of assumptions about how measurable disturbances will affect the process. Such assumptions may lose their accuracy over time, or they may fail to take into account Unexpected changes. For example, in a new engine that receives clean fuel a command to increase injection duration by a certain fraction of the crank angle will cause a certain increase in the injected amount of fuel per cycle. If 5000 hours of operation have passed since the last injector overhaul, and / or if the consistency of the fuel is not quite what it should be, the same command may cause a significant different increase in the injected amount of fuel. Mechanical wear of injectors and varying consistency of fuel are examples of non-measurable disturbances.

SUMMARY OF THE INVENTION

The following presents a simple summary in order to provide a basic understanding of some aspects of various invention embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify the key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of the exemplifying embodiments. A method, a control system, and an internal combustion engine would be needed in which control approach could take into account also non-measurable disturbances, despite being non-measurable. The control approach should be versatile so that it could be applied to controlling various processes in the internal combustion engine.

Advantageous objectives of the invention are achieved by using a primary controller for feedback-type control and a secondary controller for feed-forward-type control, and by addition making the secondary controller aware of Trends in output of the primary controller so that operation of the secondary controller can be changed in an Adaptive Manner. The desired kind of adaptation of the secondary controller can be implemented so that the aim is to maintain the output of the primary controller at a fixed value which may be zero or other corresponding "neutral" value. The neutral output of the primary controller is defined as the output of the primary controller is produced when it does not try to actively affect the state of the controlled process. Filtering, such as taking a mean or median value over a predefined time window, can be applied in order to make the adaptation of the secondary controller Concentrate on Trends in the primary controller output rather than transients.

The exemplary embodiments of the invention presented in this patent application are not to be interpreted to limit the applicability of the claimed claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated.

The novel features which are considered as characteristic of the invention are set Forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages, will be best understood from the following description of specific embodiments when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 illustrates an a prior art feedback control scheme; 2 illustrates a known combination of feedback and feed-forward control, FIG. 3 illustrates an Adaptive control system and method, FIG. 4 illustrates an example of adapting a transfer function, FIG. 5 illustrates another example adapting a transfer function, FIG. 6 illustrates another example of adapting a transfer function, and FIG. 7 illustrates the application of an adaptive control system for control Ling fuel pressure in a common rail.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Fig. 3 can be read as an illustration of a control system for an internal combustion engine by associating illustrated entities with functional blocks of the control system. Alternatively, FIG. 3 can be read as an illustration of a method for controlling a process in an internal combustion engine, by associating illustrated entities with method steps. Both interpretations are explained in more detail below.

As illustrated in fig. 3, the control system consists of a primary controller 301 that is configured to compare a feedback value to a setpoint value and to produce a primary output. The primary output is formed on the basis of said comparison; as a very simple example any change in the primary output may be proportional to the difference between the feedback value and the setpoint value. More elaborate relationships between the primary output and the result of the comparison are possible. For example, there may be a "dead zone" of very smallest comparison results that cause no change in the primary output at all, and / or proportionality (if any) between any change to the primary output and the difference between the feedback value and setpoint value may be linear, squared (and signed), or exponential, or it may have some other form.

The feedback value is an indicator of the measured dynamic quantity in a process 101 of the internal combustion engine. For example, if the dynamic quantity to be measured is the pressure, the sensor 103 is a pressure sensor that can convert the measured pressure to a corresponding voltage, current, or resistance value. The feedback value could even be a mechanical displacement, for example if the measurement of pressure was based on a reversible deformation caused by the pressure, but since the implementation of the feedback control typically involves an electronic control system, the feedback values in electric form are preferable. The secondary controller 302 is configured to receive an input value and to produce a secondary output. The words "primary" and "secondary" are just names that are used for the sake of unambiguous literal reference, and they include no connotations about e.g. the mutual significance of the control functions, or the corresponding control functions taking place in some particular order. The input value is schematically shown as coming to the secondary controller 302 from the left, and it is an indicator of a measurable disturbance affecting the process 101.

The production of a secondary output in the secondary controller 302 takes place according to a transfer function. A simple example of a transfer function is a time-independent transfer function s = s (t) according to which each input value / results in a corresponding output s. More elaborate transfer functions can be used: for example, if the output s should depend not only on input / but also at time t at which input comes to secondary controller 302, we may write the general expression s = s (t, t)

The output value s (t) to be produced at a particular time t may include the weighted sum of the current input value i (t) and some previous input values according to the general formula ΣΝ ani (t - ri) n = o where the an are summing weights and the i (t - n) are the input values at times t, (M), (t-2), ... (tN). The present invention does not place any particular restrictions on the transfer function, but in graphical illustrations and examples it is now straightforward to use a time-independent one-to-one relationship that maps each input value to the corresponding output value. The combiner 303 is coupled to receive the primary output from the primary controller 301 and the secondary output from the secondary controller 302. It is coupled to deliver a combination of them as a control signal to an actuator 104, which in turn is configured to affect the process 101. The word combination is used here in a wide sense. It may mean a simple sum of the primary and secondary outputs, or it may mean a weighted sum, a filtered sum, and / or some other result that takes into account the outputs of both controllers and has a range of possible values that is suited to drive the actuator 104 so that the desired effect on the process 101 is achieved.

The secondary controller 302 is coupled to receive the primary output as such and / or some derivative number. The word derivative as used here means "something that is derived from" and is thus not restricted to e.g. a time derivative. Examples of derivatives meant here are an example of a mean or median value of a primary output over a predefined time window.

The secondary controller 302 is configured to adapt its transfer function based on at least a portion of the target to maintain the primary output at a fixed value. This fixed value is preferably a so-called neutral value; in other words, the act of adapting the transfer function in the secondary controller aims at reaching the situation in which the primary controller would not try to actively affect the state of the controlled process 101.

Adapting the transfer function is illustrated in the following with some examples and with reference to the figs. 4, 5, and 6. In fig. 4 the leftmost case illustrates a situation where the transfer function takes the form of a rela tively smooth curve. At some point the secondary controller becomes aware that the primary output (or a derivative number as mentioned above) has the value Aj. The secondary controller is configured to respond by augmenting or scaling all the outputs given by the transfer function with constant that is equal or proportional to the value Ax (being equal is a special case of being linearly proportional, with linear proportionality constant 1). Augmenting all outputs of the transfer function by Δχ is shown in the middle part of fig. 4. If we assume that the transfer function was originally of the form s = s (i), it is now 5 = s (i) + Aj. As an alternative, if all the outputs given by the transfer function would be scaled (rather than augmented) with a constant proportional to the value A1; the new transfer function would be of the form s = aA1s (t). A combination of scaling with proportionality constant a and augmenting with proportionality constant b, the new transfer function could be expressed as s = a ^ s {i) + bA ±.

The concept of being proportional can be generalized to mean all cases where magnitude of augmentation or scaling constant increases unambiguously and monotonously with increasing values of Δ ^ Thus dependencies that qualify as proportional are e.g. linear proportionality, exponential proportionality, logarithmic proportionality, and piecewise defined proportionality.

Simultaneously the middle part of fig. 4 shows that the next value of the primary output (or a derivative number as mentioned above) is received, and has the value -Δ2. During the time period that is known to have affected the generation of this primary output, the input / to the secondary controller had some other, relatively large value, for which reason the circled-cross symbol of the newly received primary output (or derivative number) ) appears in the right-hand part of the input / output diagram. The following response of the secondary controller in adapting the transfer function is shown in the right part of FIG. 4: This time the secondary controller responds by augmenting all the outputs of the transfer function by -Δ2. Thus the act of adapting the transfer function means in this case moving the transfer function curve up or down by the amount indicated by the primary output (or derivative paragraph).

Since each step of adapting the transfer function according to the model shown in FIG. 4 moves the whole transfer function curve, it is preferable to the value on which the adaptation is based on some filtered version of the primary output value, like a mean or median value over a relatively long time window. Also, this kind of approach to adapting the transfer function is most suitable for cases in which we can reasonably be sure about the form of the transfer function, but non-measurable disturbances that are discrete by appearance and take place relatively seldom constitute a basis for the adaptation. An example of such a non-measurable disturbance could be a change in the exact Constitution of fuel. When a nearly empty fuel tank is filled to the top from a different source than before, the exact Constitution of fuel that is available to the engine may change relatively abruptly, but stays more or less the same after that, until the next fill-up .

In FIG. 5 the leftmost part illustrates the same starting point as above in fig. 4: The initial form of the transfer function is a relatively smooth curve, and the primary output value (or derivative equation) is found to have magnitude Δχ during the period of time when the characteristic input to the second controller was i ±. However, in this case the secondary controller does not start moving the whole transfer function curve. Rather, it associates received a primary output (or derivative) with a particular sub-range of input values Δί, which includes the input that was characteristic of the time over which the primary output (or derivative) was obtained. The secondary controller adapts locally the transfer function so that the outputs that the previous form of the transfer function gives for the inputs within said sub-range are augmented with values proportional to said primary output (or derivative number).

The middle part of fig. 5 shows one example of such local adapting. Within the sub-range of input values Δί, the transfer function curve is stretched so that it reaches the point that was above the original transfer function curve by Δχ. In order not to create discontinuities in the transfer function curve, the effect of adaptation is inversely proportional to the difference between the corresponding input and the characteristic input mentioned above. Another possibility would have been to cut a piece of the original transfer function curve within the sub-range of input values Δί, and to move that piece translationally upwards by Δ1; but that would naturally result in a discontinuity in the transfer function curve at both ends of the sub-range Δί.

Mathematically, the adapted transfer function could be expressed as

when ί E Δί elsewhere where t (i) is an augmentation function that is defined within the sub-range of input values M. The middle part of fig. 5 also shows that the next received primary output (or derivative) is associated with a significantly larger concurrent input value, and is below the (original!) Transfer function curve by Δ2. The rightmost part of fig. 5 shows how the transfer function has been adapted locally so that the outputs that the previous form of the transfer function gives for inputs within the appropriate sub-range (not shown separately) are augmented with values proportional to said primary output (or derivative paragraph). Again, graphically the result seems like stretching the transfer function curve so that one part of it reaches the point at which the circled-cross symbol appeared.

Repeated adaptations of the transfer function in this way will eventually adapt the transfer function to the curve so that it adapts through all points in the input / output plan for which corresponding primary output (or derivative paragraph) has been received. Such an approach to adapting is well suited for cases in which it would be difficult to define exactly the most optimal transfer function on the basis of pre-existing information only.

Figure 6 illustrates yet another example of adapting a transfer function. In this case, the secondary controller has the nature of a self-organizing map or neural network, and it is coupled to receive two different and mutually independent types of input values. In this schematic illustration, we assume that each possible pair of received values (INPUT 1, INPUT 2) makes the secondary controller produce a secondary output, the value represented by the phase angle (angle in relation to the horizontal direction to the right ) of the corresponding arrow in the drawing. The transfer function is equal to the unambiguous mapping from each possible pair of input values to the corresponding output value.

On the left in fig. 6 We assume that the primary output (or derivative sign) is received in the secondary controller, and you have received the primary output during the time period which has a particular characteristic pair (INPUT 1, INPUT 2) by point 601. We also assume that the secondary output value that was previously associated with this pair of input values was the one represented with a dashed line to the upper right from point 601. the received primary output (or derivative paragraph) defines the new secondary output value 603 in a way that is analogous to that applied above in figs. 4 and 5: it is assumed that if the secondary output had a value of 603, the corresponding primary output would have had a neutral value. A further Assumption in the left-hand part of FIG. 6 is that concept "subrange of input values" that was used in association with fig. 5 has a corresponding two-dimensional form in a self-organizing map or neural network. In other words, the effect of changing the output value associated with point 601 will "bleed" into its immediate surroundings, and cause similar (yet smaller) changes in the output values associated with adjacent points. The points that will be affected are those that fit in the Elliptical region 604. The right-hand side of fig. 6 shows the self-organizing map or neural network after the whole adaptation round has been made. Dashed lines illustrate the previous output values associated with those points for which the new output value was defined as part of the adaptation of the transfer function (note that the previous value for the actual point 601 is not shown any more because it was already shown in the left-hand part).

The mapping from two inputs to one (secondary) output in fig. 6 can be generalized so that the secondary controller can have any number of mutually dependent and / or mutually independent inputs, as long the transfer function is unequivocally defined as mapping from each possible combination of input values to the corresponding secondary output value.

Figure 7 illustrates one possible practical application of a control system described above in an internal combustion engine, such as a large diesel engine of the common rail type. On the lower right in the drawing are a fuel supply line 701 and one or more injectors 702 for injecting fuel coming from the fuel supply line 701 into cylinders (not shown) of the internal combustion engine. The dynamic quantity to be measured is the fuel pressure in the fuel delivery line 701. The sensor 103 is configured to measure the fuel pressure and provide a feedback value to the primary controller 301, which feedback value is an indicator of the measured fuel pressure. . The actuator 104 is a flow control apparatus that is configured to regulate the flow of fuel 703 into the fuel delivery line 701.

The input value to the secondary controller 302 is an indicator of the injection duration of one or more of the injectors 702. The deliberate increase in injection duration aims at increasing the output power of the engine, and requires a corresponding increase in the flow of fuel. into the fuel delivery line 701. Thus, when the secondary controller 302 receives an input that indicates an increase in injection duration, it produces a secondary output that passes through the combiner 303 to the actuator 104 and increases the fuel flow.

Non-measurable disturbances include all such factors that make this increase in fuel flow inaccurate for reasons that would be difficult or impossible to predict. For example, if the flow control apparatus is worn, a particular movement of the actuator 104 may increase the fuel flow too much or too little. Feedback control through the loop including the sensor 103 and the primary controller 301 corrects the fuel pressure, and the secondary controller 302 receives the knowledge about the need for correction in the form of the primary output that the primary controller 301 produced. If the initial increase in fuel flow was too small, the primary controller 301 produced a primary output that moved the actuator 104 a little bit further. The secondary controller 302 notices this, so it becomes aware that the next time a similar increase in injection duration is made, the secondary controller 302 should already be in the first place to move the actuator 104 a little more than before.

Similar principles can be applied to controlling various processes in an internal combustion engine. In order to ensure the applicability of the description given above, it is advantageous that if a more proactive input signal and a more reactive input signal are available, the more proactive one is used as the input to the secondary controller while the more reactive one is used a feedback value fed to the primary controller. For example, if a pilot fuel injection is used in a dual fuel engine (or pilot gas injection), the pilot fuel pressure (or pilot gas pressure) could be controlled so that information about pilot duration is used as an input to the secondary controller and a measured pressure in the pilot delivery line as a feedback value to the primary controller. Also in a dual-fuelled or gas-fuelled engine the main gas pressure control could come into question, so that the main gas duration is used as an input value to the secondary controller and the main gas pressure as a feedback value to the primary controller .

Claims (15)

A control system for an internal combustion engine, comprising: - a primary controller (301) configured to compare the feedback value to a set value and produce a primary output value based on said comparison, said feedback value being a dynamic quantity indicator of said internal combustion engine process (101) 302) configured to receive an input value and produce a secondary output value according to the transmission function of said input value, said input value being an indicator of a measurable interference affecting said process (101), and a combiner (303) coupled to receive said primary and secondary output values and supplying a combination thereof as a control signal to an actuator (104) configured to affect said process; wherein said secondary controller (302) is coupled to receive said primary output value or a derivative thereof and configured to adapt said transfer function based, at least in part, on the goal of keeping said primary output value in a fixed value. The control system of claim 1, wherein said fixed value is a neutral value. The control system of claim 1 or 2, wherein said secondary controller (302) is coupled to receive a derivative of said primary output value, which derivative represents an average or median value of said primary output value in a predetermined time window. A control system according to any one of the preceding claims, wherein said secondary controller (302) is configured to respond to a received filtered primary output value by incrementing or scaling output values provided by said transfer function with a constant proportional to said filtered primary output value. A control system according to any one of claims 1 to 3, wherein said secondary controller (302) is configured to respond to a received primary output value or a derivative thereof by associating said primary output value or a derivative thereof with a specific subvalue of input values including an input value an output value or derivative thereof was obtained, and locally adjusting said transfer function so that the output values provided by the transfer function to the input values in said sub-range are augmented by values proportional to said primary output value or its derivative. The control system of claim 5, wherein said secondary controller (302) is configured to increment output values provided by said transfer function to input values in said sub-range inversely proportional to the difference between each respective input value and said characteristic input value. A control system according to any one of the preceding claims, wherein - said dynamic quantity is fuel pressure in the fuel supply line (701), - said input value is one or more syringes (702) injecting fuel from said fuel supply line (701) into said fuel burner, - said actuator (104) is a flow control device configured to control the fuel flow (703) to said fuel supply line (701). An internal combustion engine comprising: - a fuel supply line (701), - one or more syringes (702) for injecting fuel from said fuel supply line (701) into the cylinders of the internal combustion engine, and - a control system according to claim 1, wherein said input value is an indicator of the duration of one or more of said syringes (702), and said actuator (104) is a flow control device configured to control the fuel flow (703) to said fuel supply line (701). A method of controlling a process (101) in an internal combustion engine, comprising: - measuring a dynamic quantity in said process (101) and generating a feedback value indicative of the measured dynamic quantity, - comparing (301) said feedback value to a setpoint and generating a primary output value a secondary output value according to a transfer function of an input value which is an indicator of a measurable interference affecting said process (101), - using said combination of said primary and secondary output values (303) as a control signal to actuator (104) to influence said process (101), and a derivative thereof for adjusting (302) said transfer function, at least in part, for the purpose of keeping said primary starting value at a fixed value. The method of claim 9, wherein adjusting said transfer function based on the goal of keeping said primary output value in a neutral value. The method of any one of claims 9 or 10, wherein using said primary output value or a derivative thereof comprises taking an average or median value of said primary output value in a predetermined time window. The use of any one of claims 9 to 11, wherein said primary output value or a derivative thereof is a filtered primary output value, and adjusting said transfer function comprises augmenting or scaling the output values provided by said transfer function with a constant proportional to said filtered primary output value. The process of any one of claims 9-11, wherein associating said primary output value or a derivative thereof with a specific sub-range of input values including an input value characteristic of the time period during which said primary output value or its derivative is obtained and locally adjusting said transfer function the transfer function assigns input values within said sub-range, increments with values that are proportional to said primary output value or its derivative. The method of claim 13, wherein the output values provided by said transfer function for input values in said sub-range are augmented with values inversely proportional to the difference between each corresponding input value and said characteristic input value. A method for controlling fuel pressure in a common rail injection of a common rail diesel-type diesel engine (701) according to any one of claims 9-14.