Abstract:
In a multi-cylinder internal combustion engine, equipped with an electronically controlled hydraulic system for the variable operation of the engine&#39;s inlet valves, an indicator of the differences in the amount of air aspirated by the cylinders of the engine during the respective induction phase is provided and said system controls the various inlet valves of the engine in a differentiated manner, varying the time and/or opening travel for the purpose of minimizing the differences between the amounts of air aspirated by the various cylinders of the engine.

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns internal combustion engines of the type that include an electronically controlled hydraulic system for variable operation of the engine&#39;s inlet valves. 
     In American patent U.S. Pat. No. 6,237,551, the Applicant has already proposed an engine including: 
     at least one inlet valve for each cylinder, equipped with respective elastic means of return that push the valve towards a closed position, for controlling the respective inlet port, 
     at least one camshaft for operating each inlet valve of the engine&#39;s cylinders via the respective valve lifters, each inlet valve being controlled by a respective cam of said camshaft. 
     in which each of said valve lifters commands the respective inlet valve against the action of said elastic means of return via the interposition of hydraulic means including a pressurized fluid chamber, 
     the pressurized fluid chamber associated with each inlet valve being suitable for connection via a solenoid valve to a discharge channel, for the purposes of decoupling the valve from its respective valve lifter and provoking rapid closure of the valve under the effect of the elastic means of return, and 
     electronic means of control for controlling each solenoid valve for varying the time and opening travel of the respective inlet or exhaust valve according to one or more of the engine&#39;s operating parameters. 
     In a multi-cylinder engine, the inlet ports of the engine&#39;s cylinders are connected to an inlet manifold that receives air for feeding the engine. The operating cycles of each cylinder are obviously but of phase with respect to each other, in consequence of which the induction phases occur at different times. For a series of reasons, of which the different positioning of the cylinder inlet ports with respect to the inlet duct of the inlet manifold, uneven amounts of air can be sucked into the various cylinders of the engine. 
     The object of this invention is that of resolving this problem for an engine of the type indicated at the beginning. 
     SUMMARY OF THE INVENTION 
     In order to achieve this objective, the subject of the invention is an internal combustion multi-cylinder engine possessing all of the above indicated characteristics and also characterized in that the engine has an inlet manifold, connected to the various inlet ports of the engine&#39;s cylinders, in which air-feed flow sensors are located, and in that said electronic means of control are capable of detecting the dispersion of air sucked into the various cylinders of the engine on the basis of an output signal from said sensors and for controlling the hydraulic system for actuating the inlet valves of the engine&#39;s various cylinders in a differentiated manner, in order to reduce said dispersion to a minimum. 
     In the engine in accordance with the invention, the dispersion of air sucked into the various cylinders is detected via an airflow sensor located in the inlet duct upstream of the inlet manifold. The purpose of minimizing the dispersion is to try to make the amount of air sucked in by each cylinder reach the average value of air inducted during the engine cycle. As already indicated, dispersion minimization is implemented by control differentiation and, in particular, by the opening times of the inlet valves. 
     In a preferred form of embodiment, the estimate of the dispersion of inducted air in by each cylinder with respect to the average value is obtained by evaluating the difference between the estimate of air entering the cylinder, which is based on the output signal of said sensors, and a predetermined reference value that must be reached to achieve compensation of the dispersion. 
     Always in the case of the preferred form of embodiment, the estimate of inducted air is obtained by selecting the most significant sample from those related to the induction phase of the cylinder in question. In particular, the most significant sample is that relative to the maximum value of those related to the induction phase of the cylinder under consideration. The less the inlet duct is restricted by the engine&#39;s butterfly valve, the more significant the sample is. In other words, notwithstanding the fact that the amount of air taken in by the engine can be achieved independently of the action of the butterfly valve thanks to the engine&#39;s variable valve control system control, the estimate of air entering each cylinder with the herein described method is preferably taken with the butterfly valve completely open. The reference value to be reached that is used in the above-described method is determined in a preliminary, experimental phase. Possible faults and/or malfunctions of air-induction system components that have an impact on the air taken in by a single cylinder can be diagnosed via the real-time analysis of the dispersion of air inducted by the cylinders. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
    
    
     Further characteristics and advantages of the invention will become clear from the description that follows with reference to the annexed drawings, supplied merely as a non-limitative example, in which: 
     FIG. 1 is a schematic sectional view of an engine according to known technology, which illustrates the principle of operation of the engine&#39;s variable valve actuation system, 
     FIG. 2 is a schematic view that illustrates the head of a 4-cylinder engine with the relative inlet manifold, 
     FIG. 3 is a diagram that illustrates the flow of air taken in by the engine&#39;s cylinders when actually running, before applying compensation in accordance with the invention, 
     FIG. 4 is a block diagram that illustrates the principle upon which the invention is based, and 
     FIG. 5 illustrates an alternative system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 schematically illustrates the principle of operation of a variable valve actuation system in an internal combustion engine. Reference number  1  indicates the valve (which can be either an inlet valve or an exhaust valve) as a whole, associated with a respective port  2  (inlet or exhaust) formed inside the cylinder head  3  of an internal combustion engine. The valve  1  is drawn towards its closed position (upwards with reference to FIG. 1) by a spring  4 , while it is forced to open by a piston  5  acting on the upper end of the valve stem. The piston  5  is in turn controlled, via oil under pressure that is present in the chamber  6 , by a piston  7  that supports a spring cup  8  cooperating with a cam  9  on a camshaft  10 . The spring cup  8  is held in sliding contact with the cam  9  by a spring  11 . The pressure chamber  6  can be connected to a port  12 , which in turn communicates with a pressure accumulator  13 , via the shutter  14  of a solenoid valve  15  that is commanded by the electronic means of control (not illustrated) according to the engine&#39;s operating conditions. When the solenoid valve  15  is opened, oil under pressure inside the chamber  6  is discharged, causing the valve  1  to rapidly close under the effect of the return spring  4 . 
     When the solenoid valve  15  is closed, the oil present in the chamber  6  transmits the movements of the piston  7  to the piston  5  and thus to the valve  1 , in consequence of which the position of the valve  1  is determined by the cam  9 . In other words, the cam  9  normally controls the opening of the valve  1  according to a cycle that depends on the profile of the cam, but it can be “disabled” any time it is wished by opening the solenoid valve  15 , thereby interrupting the connection between the piston  7  and the valve  1 . 
     FIG. 2 schematically illustrates the head  3  of an engine in accordance with the invention, including four cylinders  20 . An inlet port  2  and the relative valve  1  are shown for each cylinder. The inlet ports  2  branch out from an inlet manifold  21  that receives air from an inlet duct  22  in which an airflow meter  23  or flow-rate sensor is located in accordance with the invention, which is capable of generating an output signal  24  indicating the flow of inducted air passing through the duct  22 . As this phase of induction is realized at different moments in time for each cylinder  20  with respect to the other cylinders, the flow value detected by the sensor  23  is substantially representative of the amount of air taken in by the cylinder that at that moment happens to find itself in the induction phase. 
     FIG. 3 shows a diagram illustrating an example of readings taken on an engine of the type shown in FIG.  2 . As can be seen, the amount of air sucked into each cylinder is not uniform. In the case of the preferred form of embodiment, the output signal from the sensor  23 , representing the airflow (expressed in Kg/h for example) is sampled, for example, at 1 ms intervals. FIG. 3 shows that the maximum values M of inducted air for each cylinder are different from each other. 
     FIG. 4 illustrates a block diagram of the control system in accordance with the invention. Reference number  25  indicates the normal control unit that sends a signal  26  to the solenoid valves (FIG. 1) associated with the various actuators of the engine&#39;s inlet valves that cause the solenoid valves  15  to open and, in consequence, the time and opening travel of each inlet valve. This result is achieved, according to known technology, in function of a series of signals S 1 , S 2  and S 3  sent by the corresponding sensors to the control unit  25  and representing various operating parameters of the engine. On the basis of the detected engine operating conditions, the control unit  25  sends a command signal  26  to the solenoid valves, with the interposition of a diagnostics block  27 . 
     According to the invention, an auxiliary block  28  is provided for estimating the dispersion of the air entering each cylinder of the engine. Block  28  receives a signal  24  in input that is supplied by the airflow sensor  23 , as well as a signal  29 , composed of an index representing the cylinder that is in the induction phase each time. Block  28  estimates the difference in the amount of air taken in by the individual cylinders and sends to block  30  a signal  31  with the index of the cylinder under exam and a signal  32  representing the measured quantity with reference to said cylinder. The adaptive control block  30  intervenes to correct the signal  26  generated by the control unit  25 , giving rise to a corrected signal that changes the time and the opening travel of the inlet valve of each cylinder for the purpose of minimizing the detected dispersion. As has already been said, the dispersion is evaluated as the difference between a measured sample M and a predetermined reference value that is experimentally established beforehand. 
     As already said, the more the choking of the inlet duct by the engine-actuated butterfly valve is reduced, the more significant the aforesaid estimate is. Therefore, the method in accordance with the invention is preferably actuated with the butterfly valve held open. 
     As has already been indicated, the real-time analysis of the dispersion of air entering the cylinders permits the diagnosis of possible faults and/or malfunctions in the components of the air induction system that have an effect on the air entering the individual cylinders. This function is performed by block  27  in FIG.  4 . 
     FIG. 5 illustrates an alternative system in which the electronic means of control implement a strategy of compensation and diagnosis of the air taken in by the engine with independent and variable actuation of the inlet valves. This strategy includes the following operations: 
     estimation of the air aspirated by the engine, based on the measurement of airflow provided by a flow-rate sensor or airflow meter, 
     control of the average quantity of air aspirated by all cylinders using a closed-loop strategy, based on the error between the air required and the estimate of aspirated air in stationary conditions; correction occurs by adjusting the opening angles for the valves controlled in Late Opening Valve Mode or the closing angles of the inlet valves controlled in Early Closing Valve Mode, 
     storing the corrections on self-adaptive maps, also active in transitory states, 
     diagnosis of mean correct operation of the inlet valves based on the values stored in the self-adaptive maps, 
     diagnosis/identification of the correctly actuated, individual inlet valve of a cylinder; this identification is based on a reading of the value acquired by the airflow meter in fuel cut-off conditions with just one of the two inlet valves alternatively actuated. 
     Naturally, the principle of the invention being understood, the constructional details and forms of embodiment could be extensively changed with respect to that described and illustrated, by way of example, without leaving the scope of this invention.