Pressure control method and device of an intake manifold of an otto cycle internal combustion engine

Abstract

Method of controlling a pressure in an intake manifold (IT) of an Otto cycle internal combustion (E) engine, equipped with a throttle valve (TH) and an electric actuator (Act) arranged to control a target position (αdes) of a shutter (SH) of the butterfly valve and a pressure sensor (Sns), the method comprising a control procedure (CTRL) of the actuator as a function of a first pressure error between a value of target pressure ( Pd.es ) and an estimated pressure value (Pcalc), in which the estimate of the estimated pressure value (Pcalc) is a function of a second error (Ectrl) between an average value (Pmeas_filt) of the measured pressure and an average value ( Pcalc_filt) of the estimate (Pcalc) of the pressure value.

Description

Field of the invention

[0001] The present invention relates to the field of methods and devices for controlling the supply pressure measured at the intake manifold of an Otto cycle internal combustion engine.State of the art

[0002] The control of the quantity of air trapped in the cylinders of a spark ignited internal combustion engine, named with the Anglo-Saxon expression "air path control", is fundamental for the control of the torque generated by the engine itself. It is of fundamental importance for the performance of the engine as it must contribute to providing the target torque at a predetermined engine rotation speed value.

[0003] The torque generated by the engine depends on the amount of air trapped in the cylinders and the amount of fuel injected and the crank angle at which the ignition occurs, the so-called ignition advance.

[0004] Since in a spark ignition engine, the quantity of fuel is strictly related to the quantity of air trapped in the cylinders, it is understood that the control of the quantity of air entering the engine represents the fundamental factor that conditions the torque delivery from the engine. However, this amount of air trapped in the cylinders is a function of the pressure generated at the intake manifold of the engine itself.

[0005] It is immediately clear that there is a correlation between the torque delivered by the engine and the pressure generated at the intake manifold.

[0006] The pressure measured at the manifold can be influenced by the boost pressure of a possible turbocharger, however, regardless of whether the engine is supercharged or not, the pressure is controlled through the position of the throttle valve.

[0007] The intake manifold is generally associated with a pressure sensor which allows the pressure trend to be monitored at a point between the butterfly valve and the engine head. However, an engine generally comprises a discrete number of cylinders and therefore, the alternation of pumping phases between the different cylinders causes pressure oscillation. For this reason, the pressure signal generated by the sensor associated with the intake manifold is generally low-pass filtered, so as to eliminate the aforementioned oscillations. Through filtering, a signal is obtained which is generally named as "average value signal".

[0008] It is worth highlighting that a low-pass filtered signal generally coincides with the same unfiltered signal in steady-state conditions. While, in transient conditions, the two signals can also differ significantly due to the slowness with which the filtered signal varies.

[0009] The filter applied to the measured pressure signal distorts the dynamics of the measured quantity, i.e. the pressure trend inside the manifold. Therefore, the control finds itself operating with a signal that does not reflect the actual pressure conditions inside the intake manifold, especially during fast transient conditions.

[0010] This results in slow response control of the throttle valve during transients.

[0011] The filter applied to the signal representing the pressure measurement, in fact, reduces the bandwidth and therefore the system's response readiness to sudden stresses such as the step response.

[0012] It is required that the pressure control must be ready in transient conditions and, in addition, must guarantee zero and stable error in permanent and / or stationary conditions. According to the prior art, it is believed that it is more difficult to control low pressure values in steady-state conditions than high ones. The highest-pressure value is obtained when the throttle valve is completely open, therefore, the prior art tends to believe that small variations in the shutter angle have a negligible influence on the pressure value at the intake manifold compared to a condition in which the valve is close to the minimum opening condition, which corresponds to the engine idling speed. Furthermore, the known technique aims at stabilize the control of the butterfly valve, through the use of filters that slow down its dynamics. It is believed that a slower valve control ensures greater control stability.

[0013] However, by implementing the suggestions of the prior art we observed phenomena of instability of the throttle valve control and consequently of an instability of the corresponding idle speed (low idle) of the engine.

[0014] Unless specifically excluded in the detailed description that follows, what is described in this chapter is to be considered as an integral part of the detailed description.

[0015] US 2004 / 084015 A1 describes a method for controlling a pressure in an intake manifold, wherein it does not describe the specific way the estimated pressure is calculated.Summary of the invention

[0016] The aim of the present invention is to present a scheme for controlling the supply pressure of a spark ignition engine which is stable but at the same time rapid in transients. The basic idea of the present invention is to implement a control scheme that is based only indirectly on the average value of the pressure measured at the intake manifold.

[0017] More specifically, the idea is to use a model to estimate the pressure at the intake manifold, while the value of the measured pressure, appropriately filtered, is used to correct the model.

[0018] Therefore, the measured pressure value is used indirectly in its control.

[0019] The dependent claims describe preferred variants of the invention, forming an integral part of the present description.Brief description of the figures

[0020] Further objects and advantages of the present invention will be clear from the following detailed description of an example of its implementation (and its variants) and from the attached drawings given purely for explanatory and nonlimiting purposes, in which: Fig. 1 show an example of a feedback control scheme according to the present invention; Fig. 2 shows an example of a control scheme based on Fig. 1 configured to compensate for a fuel injection delay; Fig. 3 shows a spark ignition engine equipped with an intake manifold with a throttle valve and a pressure sensor connected to a processing unit implementing one of the control schemes in Figs. 1 or 2.

[0021] The same reference numbers and letters in the figures identify the same elements or components or functions.

[0022] It should also be noted that the terms "first", "second", "third", "higher", "lower" and the like may be used here to distinguish various elements. These terms do not imply a spatial, sequential, or hierarchical order for the modified elements unless specifically indicated or inferred from the text.

[0023] The elements and characteristics illustrated in the different preferred embodiments, including the drawings, can be combined with each other.Detailed description

[0024] Fig. 1 shows a feedback control scheme, in which the controlled variable is the desired value P des of the pressure at the intake manifold IT.

[0025] The block CTRL indicates any controller that returns an angle α des of butterfly valve TH actuation control as a function of the pressure error valueE ctrl .

[0026] The controller can be for example a PI or a PID combined with a flow linearization function of the butterfly valve TH. However, these are controllers within the reach of the technician in the field.

[0027] The pressure error E ctrl is given by the difference between the desired pressure value P des and the value of the pressure calculated P calc by an estimator MDL of the average pressure at the intake manifold.

[0028] The estimator MDL receives as input the signal representing the angle α des output from the controller CRTL and preferably the motor rotation speed signal "EngSs" and a quantity φ corr , which can dimensionally be a flow or a derivative of the pressure or a coefficient dimensionless.

[0029] According to a preferred variant of the invention, the estimator MDL includes a model that estimates the pressure dynamics in the intake manifold. The model can be of the "fill-empty" type which includes the speed-density and mass flow model of the throttle valve. Further models suitable for describing the pressure dynamics are known, for example based on a neuronal network.

[0030] Whatever the model implemented, it is a function of the engine rotation speed as well as additional signals typically available to the processing unit ECU.

[0031] φ corr is the output variable from a PI controller which receives as input a pressure error E mdl between the pressure signal measured at average value P meas_filt , and the pressure signal calculated at average value P calc_filt , generated by the same estimator MDL.

[0032] It is worth highlighting that both the measured pressure signal P meas by the pressure sensor Sns and the estimated pressure signal P calc generated by the estimator MDL are filtered through filters FLT identical to each other to obtain the aforementioned "average value" pressure signals. This guarantees consistency between the difference in the pressure values P calc and P meas input to the PI which generates the signal φ corr . Therefore, the estimated pressure signal P calc needs to be filtered exactly as the measured pressure signal P meas .

[0033] The error E mdl is evidently calculated on average value pressure signals. However, the estimator, receiving as input the signal representing the angle α des output from the controller CRTL and the signal of the rotation speed of the internal combustion engine, and possibly also further signals that the designer may deem useful, tries to follow the signal of the measured pressure P meas at the intake manifold, i.e. the unfiltered low-pass signal, representative of the pressure at the intake manifold.

[0034] Advantageously, the control scheme is both fast and stable. Furthermore, the PI applied to the pressure error E mdl has the aim of making the pressure signal calculated by the estimator MDL stable and with zero error, in stationary conditions.

[0035] A further control problem concerns the fact that there is a fuel injection delay that depends on the position of the crankshaft. In other words, while the pressure signal and the angle of the throttle valve shutter position are treated continuously, except for the sampling times specific to the processing unit, the injection times are calculated as a function of the position crankshaft angle. Therefore, a time lag is generated between throttle control and fuel injection timing.

[0036] Fig. 2 shows a further variant of the invention, in which two delay blocks DLY, identical to each other, are inserted immediately upstream of the actuator Act and between the output of the estimator block MDL and the filter FLT. The purpose of these blocks is to delay the signal representing the estimated pressure P calc used to produce the pressure error E ctrl and the control to the desired position α des of the butterfly valve actuator, so as to take into account the injection delay.

[0037] In fact, the injectors do not inject fuel continuously, but only when the crankshaft is in predetermined angular positions, therefore, the delay blocks DLY allow synchronizing the variation in the quantity of air trapped in the cylinders generated by the variation in pressure in the intake manifold with the relative variation of injection times and the scheduling and implementation of the injection itself. In fact, it is necessary to take into account the fact that the pressure dynamics in the intake manifold is particularly rapid, therefore, delaying the control of the valve position allows for consistency between the throttle valve control and the fuel injection.

[0038] From a control scheme point of view, the delay introduced on the control line of the actuator Act must be equal to the delay introduced immediately upstream of the filter FLT on the signal representing the estimated pressure P calc , generated by the estimator MDL, so that there is coherence between the actuator control signal and the error E mdl input to the control block PI of the estimator MDL.

[0039] It is worth highlighting that, in this case, the estimator MDL, operating on an error between average pressure values delayed due to the introduced delay blocks DLY, behaves as a predictor.

[0040] The present invention can advantageously be carried out by means of a computer program which includes coding means for carrying out one or more steps of the method, when this program is executed on a computer. Therefore, it is understood that the scope of protection extends to said computer program and further to computer readable means comprising a recorded message, said computer readable means comprising program coding means for carrying out one or more steps of the method, when said program is executed on a computer.

[0041] From the above description, the person skilled in the art is able to realize the object of the invention without introducing further construction details.

Claims

1. Method for controlling a pressure in an intake manifold (IT) of an Otto cycle internal combustion engine (E), equipped with a throttle valve (TH) and an electric actuator (Act) arranged to control a target position (αdes) of a throttle valve shutter (SH) and a pressure sensor (Sns), the method comprising a control procedure (CTRL) of the actuator as a function of a signal representative of a first pressure error (Ectrl) between a signal representative of a target pressure (Pdes) and a signal representative of an estimated pressure (Pcalc), wherein a calculation of the signal representative of the estimated pressure (Pcalc) comprises - acquisition of a signal representative of the pressure value (Pmeas) in the intake manifold using the sensor (Sns) and filtering thereof to obtain a signal representative of the average value (Pmeas_filt) of the measured pressure, - calculation of the signal representing the estimated pressure (Pcalc) in the intake manifold as a function of + a signal representative of a second error (Emdl) between said signal representative of the average value (Pmeas_filt) of the measured pressure and a signal representative of the average value (Pcalc_filt) of said estimate (Pcalc) of the pressure value, + a signal representing a value of a current position (αdes) of the shutter (SH) and + a signal representing the engine rotation speed to improve the estimate.

2. Method according to claim 1, wherein said signal representing the second error (Emdl) is previously filtered by a proportional integral controller PI.

3. Method according to claim 1 or 2, wherein said calculation procedure (MDL) of the signal representing the estimated pressure is carried out by means of a calculation model as a function of the engine rotation speed.

4. Method according to any of the previous claims wherein said control procedure (CTRL) is implemented by means of a PID type controller or a PID controller equipped with a feedback signal of a state variable and / or by means of a Feedback linearization scheme on said state variable or on a further state variable.

5. Method according to any of the previous claims, further comprising a procedure of applying a delay (DLY) to the signal representing the estimated pressure value (Pcalc) in the calculation of said signal representing said second error (Emdl) and of applying the same delay to the target position control signal (αdes).

6. Method according to claim 5, wherein said delay is a function of a signal representative of the angular position of a drive shaft (CKS) of the engine (E) and of the rotation speed of the same.

7. A computer program comprising program coding means capable of carrying out all steps of any one of claims 1 to 6, when said program is run on a processing unit operatively connected to said pressure sensor (Sns) and said electric actuator (Act) and to a signal source representing a target pressure value (Pdes) in the intake manifold.

8. Computer readable means comprising a recorded program, said computer readable means comprising program coding means capable of carrying out all steps of any of claims 1 to 6, when said program is run on a processing unit operatively connected with said pressure sensor (Sns) and said electric actuator (Act) and to a signal source representing a target pressure value (Pdes) in the intake manifold.

9. System for controlling a pressure in an intake manifold (IT) of an Otto cycle internal combustion engine (E), equipped with a butterfly valve (TH) and an electric actuator (Act) arranged to control a target position (αdes) of a throttle valve shutter (SH) and a pressure sensor (Sns), the system comprising a processing unit (ECU) configured to control said electric actuator as a function of a signal representative of a first pressure error (Ectrl) between a signal representative of a target pressure (Pdes) and a signal representative of an estimated pressure (Pcalc), wherein the signal representative of the estimated pressure (Pcalc) is, in turn, a function of a signal representative of a second error between said signal representative of the estimated pressure (Pcalc) and a signal representative of the pressure measured (Pmeas) in the intake manifold by means of said pressure sensor.

10. A control system according to claim 9, wherein said processing unit is configured to perform all the steps of any one of claims 1 to 6.

11. Vehicle equipped with an Otto cycle internal combustion engine (E) comprising a throttle valve (TH) arranged on an intake manifold and an electric actuator (Act) arranged to control a target position (αdes) of a shutter (SH) of the throttle valve and a pressure sensor (Sns), wherein the internal combustion engine comprises the control system of claim 9 or 10.

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