A SYSTEM FOR CORRECTION OF THE FUEL INJECTION TIME, UPON VARIATIONS IN ALTITUDE, FOR A HEAT ENGINE HAVING AN ELECTRONIC INJECTION SYSTEM

Abstract: A system for correction of the fuel injection time control upon variation in altitude, for a heat engine (101) having an electronic fuel injection system, and having means for substantially detecting the value of the external atmospheric pressure and for consequently correcting the value of induction air pressure utilised by a central processing unit (102) of the injection system for calculating the injection time.

Description: The present invention relates to a system for correction of the fuel injection time control upon variation in altitude, for a heat engine having an electronic fuel injection system, in particular a sequential and phased system. As is known, electronic fuel injection systems for heat engines have an electronic central control unit which, in dependence on signals which it receives from various sensors (principally sensors detecting the speed of rotation and phase of the engine, and sensors detecting the pressure and temperature of the induction air) determines for example the density of the air in the manifold and the speed of rotation of the engine so that, in dependence on the volumetric capacity of the engine itself and the desired mixture strength, calculates from an interpolation on respective memorised mappings, the phase and the injection time of the fuel at the injectors, as well as the ignition advance. The setting up and calibration of the injection system takes place at an external atmospheric pressure which is about 760 mm Hg, corresponding to a variable altitude generally up to 300 metres above sea level. During the various travels of the vehicle, at different altitudes, it can happen that as the external atmospheric pressure gradually falls (there is a reduction of about 80 mm Hg for each 1000 metres of height variation) there is an alteration of the operating characteristics of the engine, in particular of the volumetric capacity, in dependence on the different pressure losses in induction and exhaust. The phenomenum involves a variation in the mixture strength towards lean conditions which displace the slow running of the engine to lower values which are often not acceptable. The object of the present invention is therefore that of providing a system for self-correction, upon altitude variations, of the fuel injection control time so as to compensate the variations in the fuel mixture strength during journeys of the vehicle with height variations, and to maintain the operating conditions of the engine substantially independently of variations in external atmospheric pressure. According to the present invention there is provided a system for self-correction, upon variation in altitude, of the fuel injection time control for a heat engine having an electronic fuel injection system, charac­ terised by the fact that it comprises means for substantially detecting the value of the external atmospheric pressure and for correcting, consequent thereon, the induction air pressure value utilised by a central processing unit of the said injection system for calcuating the said injection time. For a better understanding of the present invention a particular embodiment will now be described, purely by way of non-limitative example, with reference to the attached drawings, in which: Figure 1 is a schematic view of an electronic injection system for a heat engine with the self-correc­ tion system of the present invention; and Figure 2 is an operating block diagram of the self correcting system of the present invention. With reference to Figure 1, there is schematically shown an electronic injection system for a heat engine 101, conveniently having four cylinders, represented partially and in section. This system includes an electronic central processing unit 102 comprising, in a substantially known way, a microprocessor 121 and registers in which are memorised mappings relating to different operating conditions of the engine 101. This central control unit 102 further includes, among other things, memory registers 109. This central control unit 102 receives signals from: a sensor 103 for detecting the speed of rotation of the engine 101, disposed opposite a pulley 104 keyed to a crankshaft 125 and carrying four teeth 131 equally spaced by 90°, a sensor 105 for detecting the phase of the engine 101, positioned in a distributor 126, a sensor 106 for detecting the absolute pressure existing in an induction manifold 107 of the engine 101, a sensor 108 for detecting the air temperature in the manifold 107, a sensor 110 for detecting the water temperature in the cooling jacket of the engine 101, a sensor 110 substantially constituted by a potentiometer, and a detector for detecting the angular position of a butterfly valve 112 disposed in the induction manifold 107 and controlled by the accelerator pedal 113: in parallel with this butterfly valve 112 there is disposed a valve 114 for the introduction of supplementary air. This electronic central control unit 102 is then connected to an electrical supply battery 115 and to earth, and, in independence on the signals from the said sensors, the operating conditions of the engine and the density of the air are utilised to determine the required quantity of fuel to be injected in dependence on the desired mixture strength. This central control unit 102 therefore controls the length of time for which the injectors 116 disposed in the manifold 107 in proximity to the induction valve of each respective cylinder are open, to control the quantity of fuel provided to the different cylinders of the engine 101 and to control the phasing of the injection by controlling the commencement of delivery of fuel with respect to the phases (induction, compression, expansion, exhaust) of the engine 101. Each injector 116 is fed with fuel through a pressure regulator 117 sensitive to the pressure in the induction manifold 107 and having a fuel inlet duct 118 for fuel coming from a pump (not ilustrated) and a return duct 119 for returning fuel to the reservoir (not illustrated). The electronic central control unit 102 is further connected to an ignition pulse control unit 120 for controlling ignition pulses which are provided to the distributor 126. The operation of the system for self-correction of the injection time upon variation in the altitude, formed according to the present invention, will now be described with reference to Figure 2, with the brief preliminary consideration that the same sensor 106 which detects the pressure of the air in the induction manifold 107 is used as the external atmospheric pressure sensor in particular operating conditions of the engine, namely with the engine stopped and with the engine under full load with the butterfly valve 112 open beyond a predetermined angular value; in such operating conditions, in which the pressure detected is sub­ stantially atmospheric pressure, calculation of a correction factor in dependence on the displacement of the external atmospheric pressure from the pressure value at sea level (the initial calibration pressure), and of a coefficient dependent on the compression ratio of the engine is enabled. This correction factor is then added to the induction air pressure value, detected by the sensor 106, to determine the necessary enrichment of the fuel mixture provided to the engine 101 so as to maintain the mixture strength substantially unvaried upon changes in altitude. With reference to Figure 2, in the programme of the electronic injection system, controlled by the microprocessor 121, at each cycle, there is a stage 10 which detects the initial condition of the stationary motor upon starting up, so as to detect if it is the first execution of the programme and if the speed of rotation (RPM) of the motor 101 is less than a predetermined minimum value (RPMO, equal, for example, to 457 revolutions per minute), and moreover to detect if the value of the air pressure detected by the sensor 106, and indicated MAPR is correct and, that is to say, less than the possible upper limit of the atmospheric pressure indicated PATMS, equal to 760 mm Hg. Upon verification of these conditions, which guarantee that the value of the pressure in the induction manifold 107, detected by the sensor 106, is substantially the same as the external atmospheric pressure, the programme passes to a calculation stage 11 for calculating a correction factor OFFMAP, which will be specified better herein­ below. If the conditions tested at the stage 10 result in a negative answer the programme passes instead to a stage 12 which tests if the motor 101 is in a dynamic operating condition, substantially at full load, such that the air pressure value in the induction manifold 107 is substantially equal to the value of the external atmospheric pressure, that is to say, if the speed of rotation RPM lies between two limit values RPM 1 and RPM 2, fixed, for example, at 100 and 1500 revolutions per minute, and moreover, if the position of opening of the butterfly valve 112 indicated FARF, is greater than a threshold angular value indicated FARF1 and corres­ ponding, for example, to an opening of 60°. In the positive case it then passes to the stage 11 for the calculation of the correction factor OFFMAP, whilst in the negative case it leads to a stage 13 which checks if the motor 101 is in another dynamic operating condition such that the air pressure value in the induction manifold 107 can still be considered substantially equal to the value of the external atmospheric pressure: this stage 13 therefore detects if the speed of rotation of the engine 101, indicated RPM, lies between two limit values RPM 3 and RPM 4, fixed, for example, at 3500 and 3700 revolutions per minute, and if the angular position FARF of the butterfly valve 112 is greater than a value FARF2 corresponding, for example, to an opening of 50°; in the positive case this leads to the calculation stage 11, whilst in the negative case, that is in the situation that the sensor 106 does not detect a pressure value corresponding to the external atmospheric pressure value, this leads to a stage 14 which puts the calculated value MPA of the induction air pressure equal to the value MAPR detected by the sensor 106. The stage 11 first of all calculates the difference (PRATC) between the greater atmospheric pressure (PATMS) and the value (MAPR) detected by the sensor 106, which is indicative of the variation of the external pressure upon variation of altitude, then tests if this difference PRATC is greater than or equal to zero, and in the contrary case fixes it at zero, and if it is less than or equal to the difference between the admissible limit value of the atmospheric pressure between sea level and the highest attainable level, indicated PATMS and PATMI, and equal, for example, to 760 mm Hg and 510 mm Hg respectively. Then the correction factor OFFMAP is calculated as a product of this difference PRTAC and a coefficient CPRA dependent on the compression ratio of the engine. From the stage 11 the programme goes to a stage 16 which calculates the pressure value MAP utilised by the central control unit 121 as a sum of the pressure value MAPR detected by the sensor 106 and the correction factor OFFMAP. From the stages 14 or 16 the programme then passes to a stage 17 which controls the subsequent operation of the programme through the microcomputer 121 for the subsequent calculations and the actuation of the sequential and phased control of the supply to the fuel injectors 116. With the described self-correction system of the present invention there is therefore an automatic adaptation of the control time of the duration of opening of the injectors in dependence on the external atmospheric pressure, upon each starting of the engine 101, by means of the stage 10, and automatically during the operation of the vehicle between different altitudes there are subsequent updating corrections by means of the stages 12 or 13 which detect the operating conditions of the enginer 101 at which the pressure in the induction manifold 107 is substantially the same as the external pressure. In all these conditions the stage 11 is thereby enabled to calculate the correction factor which is added, in the stage 16, to the signal provided by the pressure sensor 106 to provide a new calculated value of the induction air pressure such as to cause an enrichment of the mixture sent to the engine for the purpose of maintaining the mixture strength sub­ stantially constant. The advantages obtained with the self-correction system of the present system are evident from what has been described; among other things the same elements (pressure sensor 106 and central control unit 121) are utilised as are already present in the injection system itself. Finally, it is clear that the described embodiments and the illustrated characteristics of the self-correction system of the present invention can have modifications and variations introduced thereto which do not depart from the scope of the invention itself.

Claims: 1. A system for self-correction of the fuel injection time control upon variation in altitude for a heat engine (101) having an electronic fuel injection system, characterised by the fact that it includes means (10,12, 13,11,16) for substantially detecting the value of the external atmospheric pressure and for con­ sequently correcting the induction air pressure value utilised by a central processing unit (102) of the said injection system for calculation of the said injection time. 2. A system according to Claim 1, characterised by the fact that the said external atmospheric pressure value is detected via the same sensor (106) which detects the air pressure value in the induction manifold (107) of the said engine (101). 3. A system according to Claim 2, characterised by the fact that the said means include first means (10,12,13) operable to detect operating conditions of the said engine (101) in which the air pressure value in the induction manifold (107) is substantially equal to the value of the external atmospheric pressure, and operable consequently to enable second means (11) to calculate a correction factor (OFFMAP) of the induction air pressure value utilised by the central processing unit (102). 4. A system according to Claim 3, characterised by the fact that the said first means (10,12,13) detects operating conditions upon starting of the said engine (101) in which the speed of rotation (RPM) is less than a predetermined value (RPMO), or else a full load operating condition of the engine (101) in which the speed of rotation (RPM) lies within a predetermined range (RPM1,RPM2; RPM3,RPM4) and the air supply valve (112) controlled by the accelerator (113) is open by more than a predetermined angular value (FARF1; FARF2). 5. A system according to Claim 3 or Claim 4, characterised in that the said second means (11) determine the said correction factor (OFFMAP) in dependence on the displacement of the external atmospheric pressure (MAPR) from the value of the said pressure substantially at sea level (PATMS), and by a coefficient (CPRA) dependent on the compression ratio of the said engine; the said correction factor (OFFMAP) being added to the induction air pressure value (MAPR) to determine an enrichment of the fuel mixture provided to the engine. 6. A system according to the preceding Claims, characterised by the fact that the said means (10,12,­ 13,11,16) belong to a microprocessor (121) of the said central control unit (102).

Inventors: FRANCIA, PAOLO, SCARNERA, MICHELE
Applicants: WEBER S.R.L.
Application year: 1986
Main classification: F02D41
IPC codes: F02D31, F02D41