DEVICE FOR THE GOVERNING OF THE SUPERCHARGING PRESSURE OF AN INTERNAL COMBUSTION ENGINE

Abstract: The device allows the physical quantity used for the feedback-governing of the supercharging pressure of an internal combustion engine to be corrected as a function of ambient air temperature.

Description: The present invention relates to a device in use controlling the supercharging air pressure of an internal combustion engine, according to the preamble of claim 1. The trend in the internal combustion engines is presently towards increasing compression ratios to the purpose of improving the thermodynamic efficiency and reducing the fuel consumption, by resorting to turbochargers. But increasing the supercharging pressure beyond certain limits is not possible, because of the tendency of the engine to knock, especially if the fuel is not endowed with high antiknocking characteristics, as well as in order to prevent the turbocharger from exceeding the maximum allowable revolution speeds. Consequently, valves are used which are able to exhaust a portion of the supercharging air fed by the turbocharger, or valves are employed able to divert from the turbines a portion of the exhaust gases of the engine. Generally then, in the presence of knocking, the spark advance is adjusted, by delaying it, to the purpose of allowing the engine to operate under conditions far from the operating conditions which favour the knocking phenomenon. Devices for controlling the supercharging pressure of internal combustion engines are well known; both open-loop and closed-loop types thereof are currently available. The devices of the second type are more complex, but surely much more advantageous, inasmuch as they allow the supercharging pressure to be optimized through a monitoring of the actual operating conditions of the engine; to the contrary, the devices of the first type oblige the designers to adopt a fixed limit value, determined by the most unfavourable operating conditions. Also control devices of the closed-loop type are known, which comprise a programmed microcomputer (see MTZ, Motortechnische Zeitschrift, 44, (1983), 4, pages 117-120) which is able to compute, as a function of selected engine parameters, the values of a physical quantity like the supercharging pressure, as well as the values of the physical quantity for feedback-control, to the purpose of verifying whether the actual value of the supercharging pressure or of a quantity correlated to it, corresponds to the control value. The values of the above said quantities are experimentally found under the different engine operating conditions, and are those which show a determined margin of safety relatively to the values which cause a combustion with knocking, with the spark advances being optimized relatively to the same phenomenon and for fuels of determined qualities. These values are memorized in the permanent memory of the microcomputer as a function of the engine parameters preselected for defining the operating conditions of the same engine. It has been found that these devices operate efficaciously when the engines operate with an ambient temperature higher than determined values generally higher than that of ambient air under standard conditions. To the contrary, for lower temperatures a certain undesired penalization was found to detriment of the power supplied by the engine because, due to the low temperatures of intaken air and of the consequent lower temperatures of compression end, also the pressure inside the combustion chamber assumes values having wider margins relatively to those which involve the knocking. The purpose of the present invention is to provide a control device by which no noticeable reductions occur in supplied power when the temperature of intaken air decreases below a standard temperature. This purpose is achieved by a device having the features of claim 1. According to the invention, therefore, the microcomputer device of the prior art has been improved to accomplish a correction in the control values of the supercharging pressure or of the flowrate of feed air, as a function of ambient air temperature, by means of corrective coefficients stored in the permanent memory of a microcomputer and assuming increasing values, higher than 1, with decreasing values of ambient air temperature, and assuming a constant value, equal to 1, for ambient air temperatures higher than a predetermined value. Thus, with low ambient temperatures, the engine can operate with higher supercharging pressures, but with the necessary margins relatively to the knocking, and can hence supply higher powers. Indeed, DE-A-31 29 686 teaches to control the load pressure or the air intake amount in a turbocharged engine such that the nominal value of the pressure or air amount is adjustable as a function of various parameters among which also the air temperature is comprised. However, this document does not give any specific indication as to the sense or mode of performing the correction as a function of the air temperature, but limits to generically consider such a correction. Moreover, the purpose of the invention of this document is principally that of reducing the noxious emissions of the engine and not that of preventing the reduction of the supplied power at decreasing temperatures. Characteristics and advantages are now disclosed by referring to the hereto attached drawing wherein a preferred form of embodiment of the invention is shown to exemplifying, non-limitative purposes. In the figure, a supercharged engine is schematically shown which is equipped with a control device according to the invention. The engine, indicated with 10, is a four-cylinder in-line engine. The individual spark-plugs 11, 12, 13, 14 of the individual cylinders are connected with a microcomputer-control unit 18 via a distributor 15, a coil 16 and a power module 17. The control unit governs the spark advance as a function of preselected engine parameters, such as the flowrate of air fed to engine, the angle of the throttle valve(s), engine revolution speed, engine temperature, ambient air temperature, knocking, the signals of which are fed by sensors 19, 20, 21, 22, 23, 24, which are only schematically shown, inasmuch as they are per se known. Individual ducts 25, 26, 27, 28 feed air to the engine cylinders, and electroinjectors 29, 30, 31, 32 are controlled to feed gasoline into said ducts by the control unit 18, which carries out the governing of the injected gasoline amount as a function of the mentioned engine parameters. The individual ducts 25-28 branch off a manifold 33 in its turn connected to an air/air heat exchanger 34, which cools the engine supercharging air, coming from a turbocharger 35, through duct 36. Inside duct 36, a throttle 37 is provided to the purpose of choking the same air, the throttle 37 being controlled by the usual accelerator pedal, not shown. The turbocharger 35, which intakes air through an intake 38 and filter 39, is driven to revolve by a turbine 40, driven by the flue gases exhausted from the engine into ducts 41, 42, 43, 44 and into a manifold 45. In a by-pass duct 46 of the turbine 40 there is arranged a valve 47, commonly denominated as "waste-gate", actuated by a membrane-actuator 48. The actuator 48 is submitted to the difference between the atmospheric pressure, which acts on a face thereof, and the air pressure on delivery side or on intake side of turbocharger 35, which acts on its other face, as it will be better seen in the following. This pressure difference is balanced by the load of a calibrated spring 49. The actuator 48 is connected, via a duct 51, to a threeway governor electrovalve 50, which has the task of connecting the actuator 48, via duct 52, to the delivery of turbocharger 35 or, through duct 53, to the intake 36 of the same turbocharger. The electrovalve 50 is controlled, by means of lead 54, by a governor device, which is constituted by the microcomputer of the control unit 18, programmed for governing the ignition and injection of engine 10. In the permanent microcomputer memory, the computing programs which relate to the algorithms of governing of the engine supercharging pressure, and the tables of the data of the actuation quantities, of the control quantities and of the correction coefficients are contained. In the particular case, the supercharging pressure is controlled by varying the amount of the exhaust gases which bypass turbine 40, by means of the opening and the closure of waste-gate valve 47, which is controlled by the electrovalve 50. When electrovalve 50 is in rest position, it connects duct 51 with duct 52, and when it is energized, it places duct 51 in communication with duct 53. In the microcomputer permanent memory, the data is stored which relates to the energizing times and to the rest times of electrovalve 50, as a function of selected engine parameters, e.g., engine revolution speed and angle of throttle valve(s). In the same memory, also contained is the data which relates to the quantity to be controlled, e.g., the flowrate of air fed to the engine, always stored as a function of the same engine parameters, engine revolution rate and throttle valve(s) angle. The controlled quantity could be the same supercharging pressure, in which case a special detector should be provided inside manifold 33. Finally, the memory of the microcomputer contains the coefficients of correction of the controlled quantity as a function of ambient air temperature. To the purpose of carrying out the governing of the supercharging pressure, the microcomputer reads the present values of engine revolution rate and throttle(s) angle as supplied by the detectors 20 and 21, and, on the basis of the computation programs and of the data stored in its memory, computes the energizing times and the rest times of electrovalve 50 and delivers the relating signals to the same electrovalve through the lead 54. With the electrovalve 50 being in rest position, the pressure at the turbocharger 35 delivery is applied to actuator 48, and valve 47 is controlled to open duct 46; thus, a portion of engine exhaust gases bypasses the turbine 40 and the supercharging pressure decreases, due to the decreased revolution rate of the turbocharger. On the contrary, with the electrovalve 50 being energized, the pressure at turbocharger 35 delivery is diverted by the actuator 48, towards the intake of same turbocharger; thus the valve 47 remains closed and the whole volume of the flue gases flows through turbine 40. The microcomputer controls the supercharging pressure by reading inside its memory the control value of flowrate of air intaken by the engine, by means of the present values of engine revolution rate and throttle valve(s) angle. Furthermore, on the basis of the present value of ambient air temperature, supplied by sensor 23, the microcomputer determines the correction coefficient which has to be multiplied by the control flowrate value. Then, the microcomputer verifies whether the so-corrected value of the control flowrate coincides or not with the present value supplied by the sensor 19; in case of difference, it sends to electrovalve 50 the signals which allow the supercharging pressure to be decreased or increased. A similar operation procedure would be undertaken if, as the controlled quantity, the same supercharging pressure were used. In the presence of a knocking signal coming from sensor 24, the microcomputer can be programmed to undertake an action by acting first on the spark advance, by delaying it, and subsequently, should the knocking signal continue, by reducing the supercharging pressure, according to the operating way of the control device as above disclosed.

Claims: A device in use controlling the supercharging air pressure of an internal combustion engine (10), provided with at least one feed duct (36) inside which a turbocharger (35) and at least one throttle valve (37) are provided, and with at least one exhaust duct (45) inside which a turbine (40) is provided which drives the turbocharger (35), the device comprising a first valve means (47) in use controlling a bypass duct (46) of the turbine (40), an actuator (48) for said first valve means (47), sensors (19, 20, 21, 22, 24) of preselected engine parameters, a second valve means (50) operatively connected with said actuator (48), a programmed microcomputer (18) having a permanent memory storing computation programs relating to algorithms of controlling of the supercharging pressure such as to prevent knocking of the engine (10) in operating conditions, tables of data of energizing times and of rest times of said second valve means (50) memorized as a function of a pair of preselected engine parameters, and tables of data of a physically controlled quantity being either the supercharging pressure or the intake air amount, also memorized as a function of said pair of preselected engine parameters, the microcomputer (18) being programmed for determining the excitation times and the rest times of said second valve means (50) on the basis of the values of the engine parameters coming from said sensors (19, 20, 21, 22, 24) and for determining and feedback controlling the values of the controlled quantity on the basis of the same values of the engine parameters according to said stored data, characterized in that the sensors further comprise an intake air temperature sensor (23) and in that the memory has further stored correction coefficients as a function of intake air temperature, said correction coefficients assuming increasing values higher than 1 with decreasing values of intake air temperature and assuming a constant value equal to 1 for values of intake air temperature higher than a predetermined value at which a safety margin in respect of knocking is still provided, and in that the microcomputer (18) is further programmed to multiply said correction coefficients by the computed values of said controlled quantity. A device according to claim 1, wherein said actuator (48) is a membrane type actuator and the second valve means (50) is a three-way electrovalve having one way (51) connected to the actuator (48) and another way (52) connected to the delivery side of the turbocharger (35), characterized in that the third way (53) of said electrovalve is connected to the intake side of the turbocharger (35).

Inventors: CICCARONE, ANGELO
Applicants: ALFA LANCIA S.P.A.
Application year: 1987
Main classification: F02D43
IPC codes: F02D41