DESCRIPTION

The present invention relates to a system, an apparatus and a method for controlling the quantity of fuel injected into the combustion chamber of an internal combustion engine; in particular, the present invention is particularly effective in Diesel-cycle engines. The present invention also relates to a computer program comprising a plurality of instructions which, when executed on a computer, will cause said computer to carry out the steps of the method for controlling the quantity of fuel according to the present invention.

As is known, internal combustion engines, particularly Diesel-cycle ones, are characterized by the emission of polluting substances which are mostly generated by incomplete combustion of the hydrocarbons contained in the fuel injected into the combustion chamber of the engine. This incomplete combustion of the fuel injected into the combustion chamber also leads to other inefficiencies such as, for example, increased engine noise and fuel consumption.

In order to minimize such inefficiencies, the quantity of fuel delivered into the combustion chamber of the engine must be such as to minimize the presence of residual unbumt hydrocarbons at the end of the combustion process; to this end, according to techniques currently known in the art, it is possible to calculate the optimal quantity of fuel to be injected into the combustion chamber in order to minimize the quantity of unbumt hydrocarbons. The fuel injection system must therefore be so designed as to provide accurate control over the fuel injected into the cylinders of the engine.

Italian patent application IT 102016000008386 discloses a fuel injection system which can control, with a high level of precision, the quantity of fuel delivered by the injector into the internal combustion chamber of the engine. In particular, in order to ensure the utmost injection precision, such system relies on at least two pressure sensors located in the duct that supplies the fuel to the injector. However, the use of two pressure transducers per injector of the engine is a problem in terms of both production cost and system complexity. Moreover, the system disclosed in IT 102016000008386 is exclusively intended for newly designed engines, while it can be hardly implemented on existing engines.

Italian patent application IT 102017000114678 discloses an injection system comprising a single sensor, wherein the injected fuel quantity is calculated by using the “time frequency analysis” technique. Although the use of a single sensor can partly solve the above- mentioned problems, the calculation precision of such a system has proven to be insufficient to ensure a complete combustion of the fuel injected into the engine cylinders.

International patent application W02017/103803 Al discloses a method for providing feedback control over the mass of fuel injected into the combustion chamber in a common rail system, based on spectral transfer functions according to the Shin-Hammond method. Such a system is characterized by non-negligible computation complexity and poor control precision.

It is one object of the present invention to provide a system, an apparatus, a method and a computer program for controlling the quantity of fuel injected into the combustion chamber of an internal combustion engine which can overcome the drawbacks of the prior art. In particular, it is one of the objects of the present invention to provide a system, an apparatus, a method and a computer program for controlling the injected fuel quantity which is characterized by low complexity in terms of hardware and computational resources. It is another object of the present invention to provide a system, an apparatus and a method which can control the quantity of fuel injected into a combustion chamber with such a degree of precision as to minimize the amount of unbumt hydrocarbons at the end of the combustion process. It is a further object of the present invention to provide a system, an apparatus and a method for controlling the quantity of fuel injected into an internal combustion engine which can be easily implemented on existing engines.

The above-mentioned objects are achieved by the present invention through a system, an apparatus, a method and a computer program for injecting a fuel into a combustion chamber which have the features set out in the claims appended hereto, which are an integral part of the present description.

Further objects, features and advantages of the present invention will become apparent in light of the following detailed description and of the annexed drawings, provided merely by way of non-limiting example, wherein:

- Figure 1 schematically shows a system for injecting a fuel into a combustion chamber according to the present invention;

- Figure 2 schematically shows a control apparatus according to the present invention;

- Figure 3 shows a graph that illustrates an experimental correlation between the fuel mass Mmj,in entering an injector and the injected fuel mass Mmj. Describing now the annexed drawings, reference numeral 100 in Figure 1 designates as a whole a block diagram of the system 100 for injecting a fuel into a combustion chamber of an internal combustion engine.

The fuel injection system 100 according to the present invention may comprise a tank 101 in fluidic communication with an injection pump 102; according to techniques known in the art, the system 100 may further include, in order to transfer the fuel from the tank 101 to the injection pump 102, a low-pressure pump comprising a fuel filter. The injection pump 102 may be configured for raising the fuel pressure up to a predetermined value (e.g. the value of the pressure of the fuel exiting the high-pressure pump 102 may be determined as a function of the type of engine in use). For petrol engines, the fuel pressure value may be increased up to values of hundreds of bars, whereas for Diesel engines such pressure value at the outlet of the injection pump 102 may reach values of thousands of bars (e.g. 2,000 to 3,000 bar).

The system 100 further comprises a body 105 comprising an accumulation volume in fluidic communication with said injection pump 102. Said body 105 comprising an accumulation volume may either be comprised in the injection pump 102 (e.g. arranged inside the injection pump 102) or be a body separate from the injection pump 102 (e.g. arranged outside the injection pump 102). Figure 1 shows a system 100 according to the present invention, wherein said body 105 comprising an accumulation volume is arranged outside said injection pump 102. In this case, the injection pump 102 may be put in fluidic communication with the body 105 via a fuel duct 103; moreover, as schematically shown in Figure 1, the body 105 may comprise an injection rail.

The system 100 further comprises an injector 112 (also referred to as electro-injector in the present description) adapted to inject the fuel into the combustion chamber of the engine; as is known in the art, the injector 112 comprises at least one inlet 111, configured for receiving the fuel, and an outlet, configured for permitting the injection of the fuel into the engine. In general, the injector 112 can be activated or deactivated to allow or inhibit the flow of fuel from the injector 112 to the combustion chamber. In the course of the present description, the activation of the injector 112 will indicate, in general, a configuration of the injector 112 according to which the fuel is injected into the combustion chamber of the engine; conversely, the deactivation of the injector 112 will indicate, in general, a configuration according to which the flow of fuel into the combustion chamber is interrupted. For example, in Diesel-cycle engines equipped with common rail systems, the injector 112 may comprise a solenoid valve capable of closing and opening upon request. When the injector 112 is in the active configuration, the solenoid valve is open to permit the flow of fuel; conversely, when the injector 112 is in the inactive configuration, the solenoid valve is closed to prevent the fuel from flowing into the combustion chamber.

The inlet 111 of the injector 112 is configured to be in fluidic communication with said body 105; to this end, the system 100 comprises a high-pressure duct 109 in fluidic communication with both the body 105 and the injector 112. In particular, the high-pressure duct 109 is put in fluidic communication with the body 105 by means of a fluid-dynamic coupling element 108; such fluid-dynamic coupling element is configured to allow the fuel to flow from the body 105 to the high-pressure duct 109. For the purpose of reducing the pressure oscillations in the body 105 caused by the wave train triggered by the operations of the injector 112, the fluid-dynamic coupling element 108 may be so configured as to comprise a fuel passage cross-section which is smaller than the cross-section of the high-pressure duct 109. For example, the fluid-dynamic coupling element may comprise a restriction (e.g. a restriction directly formed in the high-pressure duct 109 near the body 105) or a calibrated orifice with a passage cross-section smaller than the cross-section of the high-pressure duct.

From a mechanical viewpoint, the fluid-dynamic coupling element 108 can be implemented in many different ways. For example, the fluid-dynamic coupling element 108 may be such as to provide both a fluid-dynamic coupling and a mechanical coupling between the body 105 and the high-pressure duct 109. In such a case, the coupling element 108 may be comprised in the body 105 or in the high-pressure duct 109, or, alternatively, it may comprise an element which is independent of both the body 105 and the high-pressure duct 109. In such cases, the fluid-dynamic coupling element may be a connector which is independent of both the body 105 and the high-pressure duct 109, or it may be comprised in at least one of them. Alternatively, the body 105, the high-pressure duct 109 and the fluid-dynamic coupling 108 may be produced jointly and be comprised in a single body.

The system 100 further comprises a first sensor 110 (e.g. a pressure sensor, preferably a piezoelectric or pi ezoresi stive one) capable of detecting a first flow property paown of the fuel (e g. its static or dynamic pressure) at a first measurement point along said high-pressure duct 109; according to one embodiment of the present invention, the first measurement point may be so located as to permit detecting said first flow property paownat the inlet 111 of the injector 112. The system 100 further comprises a second sensor 104 adapted to detect at least one second flow property p _ra ii of the fuel within the accumulation volume of the body 105; preferably, the system 100 may comprise a pressure control valve (PCV) 106 comprised in the body 105, configured to put the body 105 in fluidic communication with a fuel recovery duct 107 (wherein the pressure is similar to that in the tank 101) when the pressure within the body 105 reaches or exceeds a predetermined pressure threshold.

In order to provide accurate control over the quantity of fuel injected into the engine, the system 100 further comprises a control apparatus 113 configured for controlling the operations executed by the injector 112; for example, the control apparatus 113 may be configured for activating or deactivating the injector 112 for the purpose of accurately controlling the quantity of fuel injected into the combustion chamber of the engine.

Figure 2 shows a block diagram representing the control apparatus 113 as a whole, which comprises:

• a processing unit 201 (e.g. one or more CPUs);

• a memory 202 (e.g. a random access memory RAM and/or a Flash memory and/or another type of memory) operatively connected to said processing unit 113 and configured for storing at least the instructions necessary for controlling the injector 112;

• an acquisition interface 203 (e.g. a CAN-BUS interface or another type of interface) operatively connected to the processing unit 201 and configured for acquiring the first flow property paown and the second flow property praii;

• actuating means 204 (e.g. an injector drive circuit) operatively connected to said processing unit 201 and configured for activating or deactivating the injector 112 (e.g. capable of generating an electric current suitable for causing a solenoid valve comprised in the injector 112 to open or close);

• input/output (I/O) means 205 for configuring the control apparatus 113;

• a communication bus 207 configured for operatively connecting the processing unit 201, the memory 202, the acquisition interface 203, the actuating means 204 and the input/output means 205.

As shown in Figure 1, the control apparatus 113 is operatively connected to the first sensor 110, the second sensor 104 and the injector 112. According to one aspect of the present invention, the control apparatus 113 is configured for providing feedback control over the injector 112 based on an estimate of the fuel mass Minj injected into the combustion chamber. In particular, the control apparatus 113 is configured for activating or deactivating said injector 112 as a function of an estimate of the injected fuel mass Minj; in other words, the control apparatus 113 is configured for calculating, at every engine cycle, the energization timeET of the injector 112 (i.e. the time interval during which the injector 112 is active in each engine cycle) as a function of the estimated fuel mass Minj injected into the combustion chamber. For example, the control apparatus 113 may be configured for making a comparison between the estimated value of the fuel mass Minj injected into the engine during a given engine cycle and a target value M _inj (e.g. this comparison may comprise a difference between such quantities); based on such comparison, the control apparatus 113 may be configured for determining the energization time ET of the injector 112 in the next engine cycle. For example, if the estimated value of the fuel mass Minj injected during a given engine cycle turns out to be greater than a target value M _inj (i.e. the injected fuel quantity is greater than desired), then the control apparatus 113 may be configured for decreasing the energization time ET in the next engine cycle. Conversely, if the estimated value of the fuel mass Minj injected during a given engine cycle turns out to be smaller than a target value M _mj (i.e. the injected fuel quantity is smaller than desired), then the control apparatus 113 may be configured for increasing the energization time ET in the next engine cycle. According to techniques known in the art, such feedback control may comprise a Proportional-Integral-Derivative system.

It is important to note that the value of the fuel mass actually injected into the combustion chamber can be hardly measured directly during the operating phases of the engine. It is however possible, according to one aspect of the present invention, to make an accurate assessment of the fuel quantity Minj injected by the injector 112 on the basis of the fuel mass Minj.in entering the injector 112.

Figure 3 shows a graph that illustrates an example of an experimental correlation between the fuel mass Minj, in entering the injector 112 and the fuel mass actually injected into the combustion chamber (i.e. the fuel mass exiting the injector). According to techniques known in the art, this relation can be directly obtained, for example, through an experimental process comprising a plurality of preliminary measurements taken on the injection system 100 (i.e. before it is mounted to the engine), to be carried out by means of a hydraulic bench configured for measuring the fuel flow rates in and out of the injector 112. Based on such relation it is thus possible to make an accurate assessment of the fuel mass Mmj injected at every engine cycle during the operating phases of the engine as a function of the fuel mass Minj.in entering the injector 112.

It is important to point out that the relation between the injected fuel quantity and the fuel mass Minj,in entering the injector 112 can be expressed in a more complex and accurate way by taking into account additional variables such as, for example, the pressure in the accumulation chamber of the body 105. The present invention is by no means limited to the use of the relation illustrated in Figure 3; on the contrary, any relation capable of accurately expressing the correlation between the injected fuel quantity and the fuel mass Minj.in entering the injector 112 may be used, without nevertheless departing from the basic inventive idea. According to one aspect of the present invention, the control apparatus 113 is configured for determining the fuel mass Mmj,in entering the injector; to this end, the control apparatus 113 is also configured for determining a third flow property p _up of said fuel at a second measurement point along said high-pressure duct 109.

The following will describe in detail the computations made by the control apparatus 113 according to one embodiment of the present invention. To such end, the letter L will designate the distance between the first measurement point and the second measurement point, both of which are located along the high-pressure duct 109; according to one embodiment of the present invention, the first measurement point may be located at the inlet of the injector 112, while the second measurement point may be located at the fluid-dynamic coupling element 108 (in this case, the distance L between the first and second measurement points will approximately coincide with the length of the high-pressure duct 109). More generally, it is sufficient that the second measurement point is located along the high- pressure duct 109 between said fluid-dynamic coupling element and said first measurement point. The letter A will designate the cross-section of the high-pressure duct 109; the letter Cd, will designate the outflow coefficient of the fluid-dynamic coupling element 108, and the letter A _res will designate the restricted cross-section of the fluid-dynamic coupling element 108. As previously described herein, the symbol pdown, will designate the value of the first flow property, measured at the first measurement point (e.g. at the inlet of the inj ector 112 by means of a piezoresistive transducer); the symbol p _ra ii will designate the value of the second flow property measured within the accumulation volume of the body 105; the symbol p _up will designate the value of a third flow property, computed as a function of the first and second flow properties, pdown and p _ra n, at the second measurement point (e g. at the outlet of the fluid-dynamic coupling element 108).

The control apparatus 113 is configured for solving a system of equations comprising a first equation and a second equation, both of which comprise a first unknown and a second unknown; in particular, the first unknown corresponds to the fuel mass flow rate G through said fluid-dynamic coupling element 108, and the second unknown corresponds to the third flow property p _up . Note that the fuel flow rate is assumed to be positive when the fuel flows in the direction from the body 105 towards the high-pressure duct 109.

The fuel mass flow rate G through said fluid-dynamic coupling element 108 can be assessed by means of the following first equation, wherein the two formulae must be selected as a function of the time histories of p _up e p _ra u, and wherein the flow rate is assumed to have a positive sign when the fuel flows from the body 105 towards the injector 112 (i.e. when PraiA Pup): • 12 • (p _U p ^— Prail)p If Pup > Pra.il

- ⁽¹⁾ • 12 (prail ^— Pup)p If Prail > Pup where the symbol p indicates the density of the fuel.

The second equation can be expressed by combining the mass conservation equation with the motion quantity equation as follows:

According to one embodiment of the present invention, wall friction is not considered, in that it has been experimentally verified that its effect is negligible.

After multiplication by pA/L and integrating with respect to space, an ordinary differential equation is obtained: where G represents the mean flow rate calculated with reference to the spatial coordinate x along the length L. Integrating the equation (3) with respect to time, the following expression is obtained, which provides the flow rate through the duct, and which is a function of p _up (t) and pdw(t) (where paw(t) is known because it has been measured): The control apparatus 113 is configured for solving a system of equations comprising the equations (1) and (4), which are solved jointly (e g. by means of a finite difference numerical scheme).

In particular, the procedure for jointly solving the equations (1) and (4), wherein the unknowns are p _up and G, is the following: a) an initial value (at time t=0) is selected for the two unknown quantities; since before the injection starts the pressure value is virtually the same throughout the entire circuit, then p _up (t=O)= pdw(t=0), and hence G (t=0)=0 b) a discretization and linearization method is applied to the equations (1) and (4) in order to determine the time histories p _up (t) and G(t). For each time instant tj, the chosen first- attempt values of the variables p _up (tj) and G(tj) are those of the previous time instant tj.i, which are known (at time ti, the first-attempt values will be the initial ones at time t=0). At this point, it is verified whether at time tj the difference pup(tj)-p _ra ii(tj) is greater or smaller than zero, and then the correct relation is chosen in the equation (1), which is subsequently solved jointly with the equation (4). Once the two equations to be solved have been identified, the algorithm will provide new values of p _up (tj) and G(tj); if such values meet the relations under examination, then such two values will be those actually required, otherwise the procedure will be restarted using these very values as second-attempt values (the procedure will generally reach convergence after just a few iterations); c) by repeating the procedure described at b) for every time instant, it is possible to determine the time histories p _up (t) and G(t).

After having determined the time history of the pressure p _U p(t) (i.e. the third flow property p _up ), this is used in order to calculate the flow rate through the duct (i.e. the flow rate entering the injector 112). In particular, the control apparatus 113 is configured for determining a difference between the third and first flow properties, Ap=p _up -pdw. The flow rate Ginjjn through the duct can thus be determined by the control apparatus 113 as follows: where (Ap) represents the time average of Ap.

Furthermore, the control apparatus may be configured for explicitly computing the mass

Minj,in of fuel entering said injector 112 as follows:

The control apparatus 113 is therefore configured for determining, as a function of the first flow property paown (measured, for example, at the inlet of the injector 112) and the second flow property p _ra ii, the value of the third flow property p _up of said fuel at the second measurement point along said high-pressure duct 109 (e.g. at the outlet of the fluid-dynamic coupling element 108). After having determined the value of the third flow property p _up , the control apparatus 113 is configured for determining, as a function of the first flow property Pdown and third flow property p _up , the flow rate Ginj,in and/or the mass Mmj.ui of fuel entering said injector 112. Depending on the value of the flow rate Gmj,in and/or of the mass Mi _n j,in of fuel entering said injector 112 (or, in an equivalent manner, depending on the explicit value of the estimated injected fuel mass Mmj), the control apparatus 113 is configured for either activating or deactivating said injector 112.

The present invention further provides a computer program, configured for being stored in the memory 202 of the control apparatus 113, which comprises instructions adapted to control the injector 112 as described above.

It must be highlighted that this invention is also applicable to, in addition to Diesel-cycle engines, any other engine types (e.g. Otto-cycle engines, Atkinson-cycle engines or other engine types) using fuel injectors, which usually do not include the solenoid valve.

Some of the possible variants of the invention have been described above, but it will be clear to those skilled in the art that other embodiments may also be implemented in practice, wherein several elements may be replaced with other technically equivalent elements. The present invention is not, therefore, limited to the illustrative examples described herein, but may be subject to various modifications, improvements, replacements of equivalent parts and elements without however departing from the basic inventive idea, as specified in the following claims.