FR2840015A1 - Control of compression ignition internal combustion engine, uses computer control of offset in inlet and exhaust valve opening times to control combustion and levels of residual burnt gas - Google Patents

Abstract

The combustion control uses control of pressure and temperature in the combustion chamber during the compression phase and control of the mass of residual burnt gas. The control is exerted by phase offset in the opening and closing of the inlet (24) and exhaust (26) valves. The valves are controlled by a control computer (34) using a look-up table (36).

Description

Method for controlling the combustion of an internal combustion engine

  The compression ignition type and control device for implementing such a process The present invention relates to a method of controlling the combustion of an internal combustion engine of the compression ignition type. Wile also relates to a device for controlling the operation of an internal combustion engine for setting

work of such a process.

  More particularly, the invention relates to a method for controlling the combustion of a compression-ignition engine and to a corresponding control device allowing the reduction of the quantity of particles and nitrogen oxides emitted in the exhaust gas. As it is salted, the exhaust gases of internal combustion engines, in particular of the compression ignition type motor vehicles, contain harmful chemical species which are commonly treated by providing exhaust systems with treatment means, such as oxidation catalysts, particle filters, NOx traps, the function of which is essentially to transform chemical species emitted by combustion into

  non-polluting substances, or to trap these chemical species.

  Regulatory provisions tend to impose on motor vehicle manufacturers a considerable reduction in the quantities of particles and nitrogen oxide emitted in exhaust gases. The means of treatment with which the lines are provided

  exhaust cannot, by themselves, allow such a reduction.

  One of the concerns of motor vehicle manufacturers is therefore to limit the quantity of harmful particles and oxides

  of nitrogen emitted into the exhaust gases.

  In compression ignition type engines, this is generally achieved by attempting to homogenize combustion. This is achieved, on the one hand, by reducing the rich zones and, on the other hand, by diluting the air-fuel mixture, which makes it possible to reduce the maximum temperatures of combustion and thus to limit,

  in particular, nitrogen oxide emissions.

  Conventionally, this homogenization is obtained by machining the pistons, so as to obtain a predetermined compression ratio. According to this technique, the pressure and temperature conditions at the time of fuel injection, that is to say during the compression phase, wind determined by the pressures and temperatures of air intake into the engine and by the rate of geometric compression, loquel is linked to the shape of the compression chamber. For a given mass of introduced air, there is no way to vary the pressure and temperature prevailing in the combustion chamber, as well as the mass of residual burnt gases, which greatly influence the homogeneity of combustion and sure

  its timing in the engine operating cycle.

  The object of the invention is to overcome this drawback and to provide a method of controlling the combustion of an internal combustion engine of the compression ignition type, as well as a corresponding engine control device, making it possible to effectively reduce the amount of particles and nitrogen oxides emitted

in exhaust gases.

  Thus, the invention provides a method of controlling the combustion of an internal combustion engine of the compression-ignition type, for reducing the amount of particles and nitrogen oxides emitted in the exhaust gases, the engine being provided with cylinders which internally delimit a combustion chamber and which have a fuel injector and intake and exhaust valves controlled by a control computer according to

valve lift laws.

  This process comprises a phase of controlling the pressure and the temperature prevailing in the combustion chamber during a phase of compression and controlling the mass of residual burnt gases. The control of the pressure and the temperature prevailing in the combustion chamber and the control of the mass of residual burnt gases are achieved by shifting the closing phases of the

  intake valves in the law of lifting of intake valves.

  The valve closing phases are also shifted

  in the law of lifting of the exhaust valves.

  We also shift the valve opening phases

  of admission in the laws of lifting of the valves of admission.

  According to another characteristic of this process, the offset of the closing and / or opening phases of the intake valves and / or the exhaust valves is carried out according to the conditions of

engine operation.

  The instant of combustion start is preferably detected and the instants of closing of the intake and / or exhaust valves are shifted so as to cause the start

  of combustion at a predetermined time.

  According to another characteristic, the instant of starting combustion is determined according to the conditions of

engine operation.

  According to a particular mode of implementation, one implements a control of the combustion of the engine as a function of the operating conditions of the engine and a control of the fuel injection.

  for each engine operating cycle.

  The invention also provides a device for controlling the operation of an internal combustion engine of the compression ignition type, for implementing a method as defined above, the engine being provided with cylinders each delimiting a chamber. and each has a fuel injector and

  intake and exhaust valves.

  This device comprising a control computer comprising, stored in memory, laws of lifting of the valves to cause them to open and close as a function of said laws of lifting. It also comprises means for controlling the temperature and the pressure prevailing in the combustion chamber and for controlling the mass of residual burnt gas by shifting the phases of closing and / or opening of the valves in at least one of said

lifting laws.

  According to another characteristic of this device, the computer comprises a map in which the stored position values of the valves are stored as a function of parameters of

engine operation.

  Preferably, it further comprises means for detecting the start of combustion in the combustion chamber and a map in which wind stores instants of start of combustion as a function of operating conditions of the engine, the control means causing an offset. opening and / or opening phases of said valves so as to cause combustion to start in the combustion chamber at said times. Other objects, features and advantages of the invention

  will appear on reading the description which follows, given

  only by way of nonlimiting example and made with reference to the accompanying drawings in which: - Figure 1 is a schematic representation of an internal combustion engine of the compression ignition type intended for the propulsion of a motor vehicle; - Figure 2 is a diagram showing the laws of lifting the intake and exhaust valves during normal engine operation; - Figure 3a is a diagram showing laws of lifting of the intake and exhaust valves in which the closing phase of the intake valves is modified so as to control the combustion of the engine; FIG. 3b is a diagram showing another example of the law of lifting the intake and exhaust valves, the closing and opening phases of the wind being modified so as to control the combustion of the engine; s - Figure 4 is a schematic representation illustrating another embodiment of a control device according to the invention; and - Figure S shows curves illustrating modifications of the lift s laws of the intake valves according to the point of

engine operation.

  In Figure 1, there is shown a block diagram illustrating the general structure of an internal combustion engine of the compression ignition type for a motor vehicle, its means of supplying air and exhausting combustion gases, as well

than its means of piloting.

  In FIG. 1, the general numerical reference 10 designates the engine casing very schematically, which, in the example under consideration, comprises four cylinders 12 in line. Each cylinder 12 1 5 is provided with a fresh air intake duct and a duct

  of exhaust gases from combustion.

  The air intake ducts supplied with fresh air through an intake distributor 14, which is supplied by

  a pipe 16 provided with an air filter 18.

  As regards the exhaust ducts, these are connected to an exhaust manifold 20 which recovers the burnt gases resulting from the combustion of the air-fuel mixture in each cylinder 12 to discharge them into the ambient environment by a exhaust line 22, which is provided, as is conventional, with treatment means ensuring, on the one hand, a trapping of the harmful particles resulting from combustion and, on the other hand, a conversion of chemical species resulting from combustion of substances

  non-polluting by a catalysis process.

  These wind processing means constituted by conventional type processing means. They will therefore not be described in detail.

thereafter.

  However, it should be noted that they comprise an oxidation catalyst as well as so-called "active" post-treatment means such as

  than a particle filter and a NOx trap.

  The intake and exhaust ducts are each closed by at least one valve, such as 24 and 26, the lift of which is

  controlled by a camshaft, respectively 28 and 30.

  Finally, each cylinder is provided with a fuel injector, such as 32. An electronic computer, designated by the general numerical reference 34, duly programmed, manages the operation of the engine, in particular the quantity of fuel injected or [instant of ignition of the engine, so as to deliver the torque requested by the driver. In particular, the computer 34 inc incorporates all the hardware and software means for managing the operation of the engine while respecting relationships which link the angle of advance to injection to filling with air, to the dilution of recirculated burnt gases. and to various parameters, such as engine operating speed, ambient air temperature, coolant temperature,

  etc ..., as is well known to those skilled in the art.

  In particular, the computer 34 comprises, stored in memory, laws for lifting the intake 24 and exhaust 26 valves, so as to control the camshafts 28 and 30 to obtain behavior of the valves 24 and 26 correspond to laws of lifting memorized or worked out by the computer from

of these lifting laws.

  FIG. 2 shows an example of a valve lift law as a function of the angle of rotation of the camshafts 28 and

  , used in normal engine operation.

  In this figure, the term TDC designates top dead center, the term PMB designates teas dead center, the term OA designates the opening phase of the intake valves, the term OE designates the opening phase of the intake valves exhaust, the term FA denotes the closing phase of the intake valves, and the term FE denotes the phase

  closing the exhaust valves.

  In accordance with a feature of the invention, the valve actuation phases in the engine operating cycle are determined to control the pressure and temperature prevailing in the combustion chamber during compression, as well as the mass of residual burnt gases, proceeding

  to a shift of the instants of opening and closing of the valves.

  More particularly, with reference to FIG. 3a, the computer controls the pressure and the temperature prevailing in the combustion chamber during the compression phase, and therefore during the fuel injection, by acting on the closing phase of the intake valves. This command corresponds to the law used in the zone B of figure 5. In the same way, one could, as visible on figure 3b, to shift the laws of lifting of the valves of admission and exhaust. This command corresponds to the law used in zone C of FIG. 5 Likewise, the computer controls the rate of residual burnt gas by acting on the opening and closing phases of the

  exhaust and intake valves.

  More particularly, the closing phase of the inlet valves if one is shifted towards the top dead center TDC so as to reduce the pressure and the temperature in the cylinder during compression. Likewise, to increase the amount of trapped residual burnt gas, a shift is made in the closing phase of the

  exhaust valves to neutral teas PMB.

  It is thus possible to regulate and control the pressure and the temperature at the time of the injection of the fuel into the cylinders, as well as the quantity of residual gases and, consequently, adjust the delay of self-ignition so that combustion starts in all the

  operating conditions around top dead center.

  According to a first exemplary embodiment, represented in FIG. 1, the computer 34 includes, in memory, a map in which the stored position values of the valves are stored according to the operating parameters of the engine, such as the speed, the load, the pressure and temperature conditions of air admitted into the cylinders, the water temperature, etc. Thus, according to this exemplary embodiment, the computer 34 draws up control commands for the displacement of the camshafts 28 and 30 from these setpoints, depending on the engine operating point. According to another exemplary embodiment shown in FIG. 4, the computer 34 is provided with regulation means intended to regulate the combustion times around predetermined combustion times mapped in the computer 34 as a function of the

engine operating point.

  In this case, the device is provided with means for detecting the instant of combustion start. These wind detection means constituted by appropriate sensors, such as, for example, a pressure sensor mounted in one of the cylinders, an accelerometer placed on the structure of the engine or still an ionization probe, making it possible to detect [ 'instant of combustion start. The computer 34 then controls the combustion in such a way that the instant of starting of the combustion coincides with the instant of cartographic starting.

  It will be noted that, in these embodiments, the control of the

  combustion takes place over different operating cycles.

  Preferably, the computer 34 also performs a cycle-by-cycle regulation of the combustion by controlling the fuel injectors 32, so as to adjust the strategy for injecting fuel into the cylinders as a function of the engine operating point. Thus, for example, the computer 34 controls the injectors 32 so as to act on the number and the phase of the injection instants of

fuel during each cycle.

  To do this, for example, the computer 34 includes, stored in memory, a map in which the wind loads injection parameters as a function of the engine operating point. He thus directly develops piloting orders for

  injectors 32 so as to obtain a desired strategy.

  As a variant, it is also possible to implement regulation of the injection parameters using a loop of

  regulation incorporated in the computer 34.

  Referring finally to Figure S. we have represented by way of example S curves illustrating as a function of the effective average pressure (PME) prevailing in the engine cylinders, and of the operating regime, the maps of use of the laws of lifting of the conventional intake and exhaust valves (zone A), laws of lifting of modified intake valves (zone B) and laws of lifting of modified intake and exhaust valves (zone C) ). As shown in these figures, the modification of the actuation times of the intake valves, or of the intake and exhaust valves, is carried out in such a way as to reduce the emissions of particles and of oxides d nitrogen under partial load (zones B and C), without

  degrade the performance of the engine under full load (zone A).

Claims (8)

RESELL ICATIONS   1. Method for controlling the combustion of an internal combustion engine of the compression ignition type, for reducing the amount of particles and nitrogen oxides emitted in the exhaust gases, the engine being provided with cylinders (12) which internally delimit a combustion chamber and which have a fuel injector (32) and inlet (24) and exhaust (26) valves controlled by a control computer (34) according to laws of valve lift, characterized in that it comprises a phase of controlling the pressure and the temperature prevailing in the combustion chamber during a phase of compression and controlling the mass of residual burnt gases, and in that the control of the pressure and the temperature prevailing in the combustion chamber and the control of the mass of residual burnt gases are achieved by shifting the closing and / or opening phases of the intake valves and / or escape in the law of lifting of said valves.   2. Method according to claim 1, characterized in that the shift of the closing and / or opening phases of the intake valves (24) and / or the exhaust valves (26) is carried out   depending on engine operating conditions.   3. Method according to claim 2, characterized in that one detects ['instant of combustion start and one shifts the instants of closing the intake and / or exhaust valves so as to cause the start of combustion at a predetermined time. 4. Method according to claim 3, characterized in that ['instant of combustion start is determined according to   engine operating conditions.   5. Method according to any one of claims 1 to 4,   characterized in that a control of the combustion of the engine is implemented as a function of the operating conditions of the engine and a control of the fuel injection for each cycle of engine operation.   6. Device for controlling the operation of an internal combustion engine of the compression ignition type, for setting   in accordance with a process according to any one of claims 1 a   S. the engine being provided with cylinders (12) each delimiting a combustion chamber and each provided with a fuel injector (32) and inlet valves (24) and exhaust valves (26), the device comprising a control computer (34) comprising, stored in memory, valve lift laws to cause them to open and close according to said lift laws, characterized in that the computer (34) comprises means for controlling the temperature and pressure prevailing in the combustion chamber and controlling the mass of residual burnt gases by shifting the closing and / or opening phases of the valves in   at least one of said lifting laws.   7. Device according to claim 6, characterized in that the computer comprises a map (36) in which wind stored values of position values of the valves as a function of   engine operating parameters.   8. Device according to claim 7, characterized in that it further comprises means for detecting the start of combustion in the combustion chamber and a map in which wind stores instants of start of combustion as a function of operating conditions of the engine, the control means causing a shift in the opening and / or closing phases of said valves so as to cause a starting of