FR2879662A1 - METHOD FOR MANAGING AN INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

A method of managing an internal combustion engine (10) which compresses the fresh air supplying a combustion chamber (12) and wherein the valve overlap (OLv) can be varied between an intake valve (18) and an exhaust valve (22). The overlapping of the valves (OLv) is modified to use a scanning effect so that for a first gradient of at least one operating parameter, it is larger than for a second gradient of the operating parameter, the first gradient being greater than at the second gradient.

Description

Field of the invention

  The present invention relates to a method of managing an internal combustion engine which compresses the fresh air supplying a combustion chamber and in which the overlap between an intake valve and an exhaust valve can be modified.

  The overlapping of the valves according to the invention represents the simultaneous opening of an intake valve and an exhaust valve.

  The invention also relates to a computer program and an electrical memory support for an installation for controlling and / or regulating an internal combustion engine, as well as the internal combustion engine itself.

  STATE OF THE ART There are computer programs for using strategies. Internal combustion engines equipped with at least one variable exhaust valve and at least one variable intake valve are also known means. Thus, it is possible to change the opening and closing times or angle of the valves. It is also possible that towards the end of an expulsion phase (expulsion time) at the beginning of an intake phase (or admission time), the intake valve and the valve are opened. exhaust, simultaneously in the combustion chamber (overlapping valves).

  To increase the specific power of an internal combustion engine it is known to use an installation consisting of a compressor driven by a turbine installed in the exhaust pipe of the internal combustion engine and which compresses the fresh air feeding the combustion chamber. This installation is generally called exhaust turbocharger.

  In the case of an internal combustion engine that is supercharged by an exhaust gas turbocharger (gasoline engine), the power is not necessarily limited by the maximum physically possible air filling (load) as is the case typically for a motor working by suction. Moreover, in this case other operating parameters come into play and play a limiting role such as for example the maximum internal pressure allowed for reasons of resistance in the combustion chamber, and a maximum rotational speed of the turbo - exhaust gas compressor also fixed for reasons of strength, etc ...

  To obtain the desired torque, not only is the position of the throttle flap modified, as in the case of a motor operating by suction, but the supply pressure is also affected. This makes it possible to preset a desired torque as a function of the rotational speed for a certain range of speeds of rotation (or range of speeds). In many applications, it is desirable that this range of rotational speeds or range of regimes be as wide as possible so that already for relatively low rotational speeds of the crankshaft, high torque is available. For this it has proved advantageous to use a relatively small turbo-compressor. Such turbochargers make it possible to achieve, for low mass flow rates and thus at low rotational speeds, the necessary pressure gradient in the compressor to obtain high torque. Another advantage is that the moment of inertia of the turbine is low which allows to very quickly reach the supply pressure.

  But a disadvantage is that the flow of such a turbocharger is limited because of the limitation of the rotational speed of the turbine which limits the maximum power that can provide such an internal combustion engine. If instead of this small turbocharger is used a larger turbocharger, there will certainly be a higher possible maximum power than for a relatively small turbocharger but for low rotational speeds, the mass flow is not sufficient to ensure the desired compression. In addition, such a turbocharger requires a relatively long time because of the large moment of inertia of the turbine to accelerate from a low regime to a high regime; this makes the internal combustion engine take a long time to provide the desired power. This effect is noticeable especially at low crankshaft rotation speed is called turbocharger hole.

  In addition, it is generally known that the opening angle and the closing angle of the intake valves and the exhaust valves have a significant influence on the air filling of the combustion chamber. . The possibility of modifying the overlap of the camshafts is also known and allows in certain operating situations of the internal combustion engine particularly at low rotational speeds with at the same time a high load, to ensure a scan of the combustion chamber. with upstream of the intake valve, a higher pressure than downstream of the exhaust valve. This difference in pressure and the simultaneous opening of the intake and exhaust valves accentuate the sweeping effect of the combustion chamber with the fresh air and increase the charge or air filling. This results in a larger mass flow of exhaust gas and depending on the design of the exhaust gas turbocharger this can result in a greater pressure gradient in the compressor. As a result, there is an increase in the torque. Thus, one can have either a higher torque for the same supply pressure or the same torque for a lower supply pressure.

  In the case of an internal combustion engine that compresses the fresh air supplying the combustion chamber, different possibilities and strategies are available in a speed / load range, given to obtain the desired torque (setpoint torque).

  According to a first strategy, the optimum criterion that is to say the desired torque can be obtained with a fuel consumption as low as possible. It has been found that this objective is best achieved if the overlap of the valves, that is to say the duration of simultaneous opening of the intake valve and the exhaust valve is relatively small and if at the same time the supply pressure is relatively high or just high enough to reach the desired torque. This strategy will be referred to hereafter as STRAT1.

  According to another strategy, the optimization criterion is that of a response that is as good as possible. In the case of internal combustion engines equipped with a turbocharger, this is a problem currently because the usual turbochargers do not provide the supply pressure necessary to obtain a certain torque only with a certain delay after having expressed the corresponding power demand. This problem is all the more noticeable since the desired power gradient is important and the desired power must be provided quickly (the power gradient means in the present description either directly the variation of a power as a function of time, or indirectly the variation over time of an operating parameter of the internal combustion engine which influences the power).

  For this purpose (ie to have a good answer), it is recommended to operate the internal combustion engine by applying the sweeping effect described above and for this purpose by realizing an important overlap of the trees. with cams. Thus, for a low supply pressure, a large amount of fresh air will arrive in the combustion chamber of the internal combustion engine and give the same torque. The time required to reach this lower supply pressure is then shorter which results in a reduction of the turbocharger hole. This strategy will be referred to hereafter as STRAT2.

  The comparison between the STRAT1 and STRAT2 strategies showed that the specific fuel consumption for the STRAT2 strategy as a function of the exhaust strategy was higher. OBJECT OF THE INVENTION The object of the present invention is to develop a method of the type defined above so that an internal combustion engine equipped with an exhaust gas turbocharger supercharging exhibits a better response behavior. that is to say, transforms as quickly as possible a demand for power while having an advantageous fuel consumption.

  DESCRIPTION AND ADVANTAGES OF THE INVENTION To this end, the invention relates to a method of the type defined above, characterized in that the overlapping of the valves is modified to use a scanning effect so that for a first gradient of at least an operating parameter, it is larger than for a second gradient of the operating parameter, the first gradient being greater than the second gradient.

  If one has a high gradient, it means that the power must be increased rapidly and thus the internal combustion engine will work with the STRAT2 strategy. On the other hand, for a low gradient, if the internal combustion engine operates for example at constant power, the strategy STRAT1 will be applied.

  According to a first advantageous development of the method of the invention, the operating parameter is a position of a control element by which the user expresses his power demand. Such a control element is for example the accelerator pedal of a motor vehicle equipped with this internal combustion engine. If the control element is actuated quickly, it means that the user wants a rapid variation of the power of the internal combustion engine. The actuation speed of the control element can be determined in a very simple manner which makes an economic realization of the method of the invention possible.

  As operating parameters it is also possible to envisage a setpoint torque, a setpoint supply pressure, a setpoint air filling or a target fuel quantity. In this case, the gradient can be determined indirectly from the deviation between a setpoint operating parameter and the actual value of this parameter. If the difference or deviation is relatively large, it will take a large gradient to reduce as quickly as possible this deviation or difference between the set value and the actual value. Such nominal quantities and actual quantities, such as, for example, the torque and the supply pressure, usually exist in motor controls, so that their use in the method according to the invention is possible without great difficulty.

  A particularly simple embodiment of the method of the invention is characterized in that if the gradient and / or deviation between the setpoint operating parameter and its actual value reaches an upper limit value and / or exceeds it, the STRAT2 strategy (significant overlap of the valves). This delivery as fast as possible of a desired power can be achieved simply in this process.

  Similarly, it is proposed that if the gradient and / or the deviation reaches a lower limit value or falls below it, the strategy STRAT1 (small overlap of the valves) is applied.

  According to this development of the method of the invention, it is simple to select the strategy for the internal combustion engine that ensures the most favorable fuel consumption. The lower limit value may depend on the amplitude of the operating parameters, which again results in an optimization of the process.

  Drawings The present invention will be described below in more detail with the aid of an exemplary embodiment shown in the accompanying drawings in which: - Figure 1 is a schematic view of some components of an internal combustion engine, FIG. 2 shows four diagrams representing the supply pressure, the overlapping of the valves, the difference between a setpoint torque and a real torque and a speed of actuation of the accelerator pedal as a function of time; FIG. 3 shows a flow chart of a method for managing an internal combustion engine according to FIG.

  Description of the embodiment of the invention

  According to FIG. 1, an internal combustion engine generally bears the reference 10. This internal combustion engine comprises several cylinders with combustion chambers, but FIG. 1 only shows one cylinder with a combustion chamber bearing the reference 12. The combustion chamber 12 is delimited by a piston 14 cooperating with a crankshaft 16. The fresh air arrives in the combustion chamber 12 through an inlet valve 18 connected to the pipe 20. The hot combustion gases are evacuated by the exhaust valve 22 and an exhaust pipe 24 out of the combustion chamber 12. The intake valve 18 is controlled by an intake camshaft 26; the exhaust valve 22 is controlled by an exhaust camshaft 28. The intake camshaft 26 is connected to a camshaft adjuster 30; the exhaust camshaft 28 is connected to a camshaft adjuster 32.

  The combustion chamber is equipped with an injector that injects the fuel directly. But in principle, one could also consider installing an injector 34 in the intake pipe 20 (this variant is shown in Figure 1). The air / fuel mixture in the combustion chamber 12 is ignited by a spark plug 38. Upstream of the intake valve 18, the intake pipe 20 comprises a throttle flap 40. This adjusts the mass of the fuel. air in the combustion chamber 12.

  Upstream of the throttle flap 40, the intake pipe 20 comprises a compressor 42 which compresses the air intended for the combustion chamber 12. The compressor is mechanically driven (reference 44) by a turbine 46 installed In the exhaust pipe 24. Upstream of the turbine 46, there is a valve installation 48, also known as the exhaust port, by which the turbine 46 can be bypassed with the exhaust gas. The combination formed of the compressor 42 and the turbine 46 will hereinafter be called turbocharger.

  The operation of the internal combustion engine 10 is controlled or regulated by a control and regulating installation 50. Thus, for example, the throttle flap 40, the injector 34, the two control installations of the camshaft 30, 32 and the exhaust door 48 are controlled by the control and regulating installation 50. The input signals are supplied to the control and regulating installation 50 by different sensors such as, for example a rotational speed angle sensor 52 which detects the current rotational speed position of the crankshaft 16. In addition, an air mass flow meter 54 provides signals to the control and regulating installation 50 which determines the speed of rotation. air mass for the combustion chamber 12. Fig. 1 also shows a position sensor 56 which captures the position of the accelerator pedal 58. The accelerator pedal 58 is a control element by which aFor example, a user of a motor vehicle (not shown) equipped with the internal combustion engine 10 makes it possible to request the power.

  In order to carry out a strategy of operation STRAT2, a large valve overlap is required, which means that at the transition between the expulsion phase and the intake phase, the intake valve 18 and the valve must be opened simultaneously. 22 as is already described above, the pressure gradient between the intake pipe 20 and the exhaust pipe 24 is achieved by appropriate control of the camshaft adjusters 30 and 32. results in a sweeping effect. To achieve the STRAT 1 strategy, small valve overlaps and a higher supply pressure are set to obtain the desired torque. This is ensured by the control of the exhaust door 58.

  The operation of the internal combustion engine 10 according to the two strategies STRAT1 and STRAT2 described will be explained hereinafter with reference to FIG. 2. In this figure, as a function of time, the supply pressure PM, the overlap of valve OLv between the intake valve 18 and the exhaust valve 22, the deviation dM between the target torque and the actual torque and the speed dwped / dt (position gradient) corresponding to the actuation of the pedal d accelerator 58.

  First of all at the instant to the accelerator pedal 58 is fixed and the difference dM between the actual torque and the target torque is virtually zero. In this essentially stationary mode of operation of the internal combustion engine 10, the camshaft adjusters 30 and 32 are set by the control and regulating apparatus 50 to have a relatively small valve overlap OLv having the value OLv1 (STRAT1). To obtain the desired torque, a supply pressure PM of level PM1 is required.

  At time t1, the driver of the internal combustion engine 10 suddenly depresses the accelerator pedal 58 so that the gradient or speed dwped / dt at which the accelerator pedal 58 is depressed exceeds a limit value G1 . In the following, the setpoint torque to be provided by the internal combustion engine 10 increases which results in an increase in the torque deviation dM. If the deviation dM between the setpoint torque and the actual torque exceeds a limit value G2, the control and regulating installation 50 recognizes a dynamic operation of the internal combustion engine 10; in other words, the installation assumes that the torque must increase rapidly, that is to say with a high gradient.

  In the following, the overlap of the valve OLv is increased to go from the value OLv1 to the value OLv2 (STRAT2). This means that to obtain the setpoint torque no PM supply pressure of PM3 value but only PM2 value is required. Ain-si, the time required for the supply pressure to change from the value PM1 to the value PM2 will be shorter. This duration is referenced dti in Figure 2 and is called the hole of the turbocharger.

  FIG. 2 shows that this turbocharger hole would be much larger (period dt2 in FIG. 2) without increasing the overlap of the valves OLv. When the supply pressure PM reaches the value PM2, the deviation dM between the actual torque and the target torque falls below a limit value G3. Since the gradient dwped / dt is again close to zero, the control and regulating installation 50 controls that the overlap OLv decreases from the value OLv2 to the value OLv1 (STRAT1). This reduction, however, occurs gradually and in all cases much more slowly than the increase which consisted in passing from the OLv1 value to the OLv2 value. The PM supply pressure required to obtain the desired target torque increases accordingly and changes from PM2 to PM3; this may first result in a slight increase in the deviation dM between the actual torque and the target torque. i0

  It should be noted that in FIG. 2, the pressure PMO is the supply pressure that must be obtained if, in the stationary mode, at time t0, it is desired to obtain the desired target torque with a large valve overlap OLv OLv2 level (STRAT2). It should be noted that the PMO value is lower than the PME value which would give a turbocharger hole dt3 slightly greater than the turbocharger hole that is reached if one changes from a STRAT operating strategy to a low valve overlap mode. dynamic to a STRAT2 operating strategy with high valve overlap.

  The flowchart of FIG. 3 describes a method for managing the internal combustion engine 10 of FIG. 1. After the starting block 60, firstly, the operating strategy STRAT 1 for which the internal combustion engine is passed 10 operates with low valve overlap (block 62). Block 64 de-mande if the gradient dwped / dt of the position of the accelerator pedal 58 is greater than a limit value G1. If the answer in block 64 is affirmative, then in block 66 it is asked whether the difference dM between the actual torque and the target torque of the internal combustion engine 10 is greater than a limit value G2. If in this case also the response is positive, then in block 68 the operating strategy STRAT2 for which the internal combustion engine operates with a larger valve overlap is initialized. If the response given to blocks 64 and 66 is negative each time, it returns to the input of block 62.

  In block 70, it is asked whether the difference dM of the actual torque and the target torque is less than a limit value G3. If this still is not the case, we return to the input of the block 68 that is to say that the internal combustion engine 10 continues to operate according to strategy STRAT2 (significant overlap of the valves). If, on the other hand, the response in block 70 is affirmative, it returns to the input of block 62 and the internal combustion engine 10 again operates with STRAT1 (low overlap of the valves). It is possible that the lower limit value G3 depends on the target torque level or in other words: the changeover to the STRAT 1 operating strategy occurs if the target torque has reached a certain percentage of the actual torque or at least tries to reach it.

  To reduce the turbocharger hole mentioned above, we can consider different concepts. One measure is for example to establish as quickly as possible the supply pressure for example by using complementary electric compressors. Another way is to assist the internal combustion engine with an external electric motor.

  At present, a strategy is applied using the sweeping effect, known per se only in situations in which the turbocharger hole must be reduced. An internal combustion engine operating schematically to the advantage of a very good behavior in response and at the same time that of an advantageous fuel consumption by the internal combustion engine in many operating situations. Another important advantage is that it does not require additional accessories as is the case in other concepts. This translates into a significant saving.

Claims (11)

  A method of managing an internal combustion engine (10) which compresses the fresh air supplying a combustion chamber (12) and wherein the valve overlap (OLv) can be varied between an intake valve (18). ) and an exhaust valve (22), characterized in that the overlapping of the valves (OLv) is modified to use a sweeping effect so that for a first gradient of at least one operating parameter, it is larger only for a second gradient of the operating parameter, the first gradient being greater than the second gradient.   2) Method according to claim 1, characterized in that the operating parameter is a position (wped) of a control element (56) by which the user expresses his power demand.   3) Method according to claim 1, characterized in that the operating parameter is a setpoint torque and / or a setpoint supply pressure (pM).   4) Process according to claim 1, characterized in that from a deviation (dM) between a real torque and its design torque or a real supply pressure and its nominal supply pressure, it is concludes with the gradients.   5) Method according to claim 1, characterized in that if the gradient and / or a deviation (dM) between the actual torque or the actual supply pressure and its setpoint torque or its target supply pressure reaches a first upper limit value (G1, G2) and / or exceeds it, the valve overlap (68) is increased.   6) Method according to claim 1, characterized in that if the gradient and / or the deflection (dM) reaches or falls below a lower limit value (G3), the valve overlap (62) is reduced.   7) Method according to claim 6, characterized in that the lower limit value (G3) depends on the amplitude of the operating parameter.   8) Computer program, characterized in that it is programmed to apply a method according to any one of the preceding claims.   9) Electrical storage medium for a control and / or regulation installation (50) of an internal combustion engine (10), characterized in that it contains the recording of a computer program for the application of a method according to any one of claims 1 to 7.   Control and / or regulating installation (50) of an internal combustion engine (10), characterized in that it is programmed to apply a method according to any one of claims 1 to 7.   11) Internal combustion engine (10), in particular for a motor vehicle having a control and / or regulating installation (50) programmed to apply a method according to any one of claims 1 to 7.