FR2812912A1 - METHOD AND DEVICE FOR IMPLEMENTING A HEAT ENGINE - Google Patents

Abstract

Method for implementing a heat engine operating according to at least two operating modes, according to which an operating mode is selected and this operating mode will only be authorized if the torque requested from the heat engine can be achieved while respecting the limits of the air / fuel ratio for this operating mode, the maximum possible torque is determined at the limit of the air / fuel ratio for this operating mode and a signal to release the operating mode is reset if the torque requested cannot be achieved while respecting the limits, characterized in that the requested torque is the setpoint torque that must actually be adjusted.

Description

STATE OF THE ART The present invention relates to a method and a

  device for implementing a heat engine operating according to at least two operating modes, according to which an operating mode is selected and this operating mode will only be authorized if the torque requested from the heat engine can be achieved while respecting the limits of the air / fuel ratio for this operating mode, the maximum possible torque is determined at the limit of the air / fuel ratio for this operating mode and a signal to release the operating mode is reset if the torque requested

  cannot be achieved while respecting the limits.

  Direct petrol injection heat engines operate according to at least two operating modes between which one switches according to at least one release signal. These modes

  of operation are in particular the homogeneous mode and the stratified mode.

  Such a procedure is for example described in the document DE-

  A 198 50 584. This operating mode is selected according to the indication provided by a field of operating characteristics according to the operating state of the heat engine. In addition, the signal to release the current operating mode is, among other things, reset to zero (and one switches to the other operating mode) if this operating mode cannot provide the requested torque while respecting predetermined limits for the ratio. air / fuel (limit value of the Lambda coefficient). This is how, for example, in such a case, if one is in laminated mode, the release signal from the laminated mode will be reset.

  and we will switch for example to the homogeneous mode.

  The realization of this liberation is done by a comparison of the couples. A limit value of the Lambda coefficient valid for this operating mode is predetermined (for the stratified mode, it is a minimum value) from which a minimum or maximum Lambda efficiency is deduced. In all cases, for the air load (set load) to be set for this operating mode, an optimum torque is deduced from a field of characteristics depending on the speed of rotation (speed) and that is specific to the operating mode. This characteristic field is loaded with data for certain standard conditions also relating to the air / fuel ratio, so that the Lambda efficiency mentioned above represents the deviation of the torque compared to a normalized value for a certain deviation of the Lambda coefficient. By combining the Lambda efficiency with the optimum torque, a minimum or maximum possible torque is formed for this operating mode. The maximum possible torque also represents the torque obtained for the desired target load, and (taking into account the Lambda limit), the maximum possible, stationary, fuel supply. We

  compares this maximum possible torque with the requested setpoint torque.

  If the requested setpoint torque is less than the maximum possible torque, the operating mode remains released, because the torque requested for this operating mode can be obtained within

predetermined Lambda limits.

  The release of the operating mode as it was

  described above is done on the basis of the desired target filling.

  However, there are operating modes in which the torque of the heat engine is mainly fixed by the fuel solution. The procedure presented to release the operating mode thus assumes that the torque achievable by the fuel solution corresponds to the torque desired by the air solution. However, if the torque corresponding to the fuel solution differs from that of the air solution in a stationary manner, this means that the stationary operating limits are permanently exceeded. This can for example be the case if for a long period there is an increase in the demand for torque depending on the fuel solution by the idling control. This results in a strong enrichment due to the increase in fuel supply and produces the stationary overshoot of the Lambda limit. This state can certainly be tolerated briefly, in dynamic mode but not over an extended period, because the consequence of exceeding this limit (also called combustion limit)

  may result in the formation of soot and / or misfires.

  Document DE-A 197 28 112 describes a control system for a heat engine with direct fuel injection on the basis of the torque. For this, the torque is adjusted in homogeneous throttled mode as is known in conventional control systems, on the basis of the torque demand using the air solution and the indication of the predetermined air / fuel ratio (in general this ratio is stoichiometric) to obtain the quantity of fuel to be injected. In the presence of conditions corresponding to the laminated mode, the operating mode is switched, that is to say that the laminated operating mode is released. In this operating mode, the torque demand is fixed by the fuel solution, the throttle flap

  (butterfly) being essentially open.

  Advantages of the invention By taking account of the torque demand, by using the fuel solution to determine the release signal of an operating mode in particular of the stratified mode or of another operating mode in which the engine must operate without being strangled, a prolonged, lasting overshoot of the stationary operating limit is effectively avoided, and thus a possible formation of soot or

misfires.

  It is particularly advantageous to check the torque actually requested to check whether it can be obtained in the desired operating mode, only if the

  stationary operating limits.

  Drawings The present invention will be described below using embodiments shown diagrammatically in the accompanying drawings, in which: FIG. 1 is a block diagram of an overall installation for controlling a motor thermal with direct petrol injection, - Figure 2 shows a flow diagram for the formation of a release bit for an operating mode for example the

laminate mode.

  Description of the exemplary embodiments

  FIG. 1 shows a control unit 10 comprising

  as elements at least one input circuit 12, at least one micro-

  computer 14, an output circuit 16 and a communication system 18 bringing these elements together. The input circuit 12 receives the input lines through which the signals from the corresponding measurement installations representing the operating parameters arrive or from which these operating parameters are deduced. It is for example an input line 20 connecting the control unit to a measuring installation 22 which determines a quantity representing the degree of actuation [of the accelerator pedal, an input line 24 which comes from a measuring installation 26 and providing a quantity representing the engine rotation speed (speed) Nmot, an input line 28 by which the control unit 10 is connected to a measuring installation 30 providing a signal representing the mass of HFM supply air. In addition there are input lines 36-40 which supply other signals from the measuring installations 42-46 representing operating quantities. For example, such operating variables used for controlling the heat engine, there are temperature variables, the position of the throttle flap (butterfly), the composition of the exhaust gases, etc. To control the heat engine, according to the embodiment of FIG. 1, the output circuit 16 is connected to output lines 48-52 to control the injectors 54 as well as an output line 56 to control a shutter d 'throttle 58 adjustable by an electric motor. In addition (this is not shown for reasons of

  simplification of the drawing), the ignition angle is controlled.

  To control the heat engine, a torque request is formed by combining different internal and / or external torque requests to form a resulting torque request for the heat engine. Examples of such requests are requests from the driver, requests from external systems such as traction control etc. The torque demand conversion is done differently depending on the operating mode chosen for the engine. In homogeneous mode, the resulting setpoint torque is distributed between the filling solution which reacts slowly and the synchronous solution to the crankshaft, acting quickly; the filling solution is the main solution and regulates the stationary torque. From the torque, a set point filling is calculated, regulated by the throttle valve adjustment. In the synchronous solution to the crankshaft, by influencing the instant of ignition and / or the dosage of the

  fuel, the desired torque is dynamically adjusted.

  Similarly, in the stratified mode, the resulting setpoint torque is distributed between the filling solution, reacting slowly and the synchronous solution at the crankshaft reacting quickly. In this

  case, the synchronous crankshaft solution is the main solution.

  As for reasons of loss, the throttle flap must be opened as large as possible, the set point filling is carried out in laminate mode and thus the throttle flap is adjusted not according to the indication of the set point torque, but according to indication of the minimum vacuum required in the suction pipe. The torque is then transformed by determining the mass of fuel to be injected. The same remark applies to the other operating modes with a strangled mode corresponding for example the homogeneous lean mode. The additional function output signals such as for example an idle speed control are combined at least in non-throttled mode with the setpoint torque for the quick solution (fuel solution) and can thus stationary modify the setpoint torque, in particular increasing it. The current operating mode is selected using an operating mode characteristic field; depending on the speed and the load or the torque, the current operating mode is selected. This selection is imposed in certain circumstances of high priority. One such circumstance is that of the torque requested in the selected operating mode which cannot be adjusted within the limits of the Lambda limits. If this is the case, the release of the current operating mode is reset to zero, that is to say that this operating mode is prohibited and a switch to another operating mode is made. In this context, a release signal is formed which takes a value releasing the respective operating mode if the requested torque is adjustable in this operating mode while respecting the Lambda limits. The formation of this signal and thus the release or prohibition of an operating mode will be described below using

  of the diagram shown in Figure 2.

  The flow diagram shown in FIG. 2 outlines a program executed in the calculation unit of the control unit 10. The elements used and the symbols then represent program steps or parts of a program while the lines of

  link represent the transmission of information.

  The program shown in Figure 2 shows the formation of a release signal B_schen for the stratified mode of a direct injection petrol engine. For the other operating modes, there are suitable programs and the formation of corresponding release signals, adapting the limit values

and signals.

  The release signal B_schen is formed in a comparator 100 which compares the maximum possible torque MIMAXSCH while respecting the Lambda limits in the current operating mode and the requested torque MIENSCH (setpoint torque). The maximum torque MIMAXSCH at the basis of the torque comparison 100 is formed from an optimum torque for the stratified MIOPTSCH mode and the Lambda ETALAMSCH efficiency for the minimum possible Lambda value at the combination point 124 (multiplication point). Lambda efficiency is formed from the performance characteristic field 126 with indication of the minimum possible Lambda value LAMBDAMINSCH; the optimum torque is obtained from a characteristics field 128 according to the engine speed NMOT and the reference filling (reference charge) RLSOLL. In other operating modes, other fields of characteristics are used,

  characteristic curves and sizes.

  The torque requested MIENSCH on the basis of the torque comparison generally represents (see the position shown in solid lines of the switching element 102), the stationary torque MISOLLLUFT, desired by the air solution. As indicated above in an application, it was found that this procedure resulted in certain unfavorable circumstances in a prolonged exceeding of the combustion limit, stationary and thus in the formation of soot or even misfires of combustion. To avoid this situation, the switching element 102 is switched in certain circumstances to the position shown in broken lines so that the torque request signal MIENSCH on the basis of the comparison 100 is formed from the request signal of the MISOLLKR fuel solution. In certain operating situations, this torque may be different from that requested by the air solution, since additional functions such as, for example, idling control are combined with the torque request signal corresponding to the fuel solution, for example by channel.

  additive and thus increase this torque.

  The switching element 102 is switched when a prolonged overshoot of the stationary Lambda limit is detected for a high torque demand. For this, in a comparator 104, the minimum possible Lambda value is compared in LAMBDAMINSCH laminate mode with the LAMBDASCH setpoint Lambda limit for the limited setpoint Lambda value in the dynamic range possible according to the torque structure, in laminate mode. If the latter exceeds a minimum value, the comparator 104 generates a signal applied to the AND combination 106. Correspondingly, in a comparator 108, the torque requested for the MISOLLKR fuel solution is compared to the requested torque MISOLLLUFT for the air solution. If the torque requested MISOLLKR for the fuel solution is greater than that of the air solution MISOLLLUFT, the comparator 108 also generates a signal applied to the point of combination ET 106. If the two conditions exist, the combination ET 106 gives an output signal applied to another ET 110 combination. The presence of an output signal from the ET 106 combination means that the stationary Lambda limit is exceeded below for a high torque demand for the fuel solution, that is to say a torque request by the fuel solution located above the torque that one wishes to achieve by

air solution.

  The AND combination 110 combines the output signal of the AND combination 106 with the status signal B_sch indicating whether or not the current operating mode is the stratified mode. If it is stratified mode, this signal is positive, so that in the presence of an output signal from the combination ET 106, there will also be an output signal to the combination ET 110. This signal sets the flip-flop function 112 in the state. In order to switch the signal at the base of the torque comparison only if the overshoot below the Lambda limit is prolonged for a long time with a high torque demand, a timer element 114 is further provided which delays the output signal of the flip function. -flop 112. The output signal of the timing stage 114 then switches the switching element 102 if necessary to the position

  shown in broken lines.

  The resetting of the flip-flop function 112 and thus that of the switching element 102 takes place under different conditions; on the one hand, this occurs if one has not gone below the Lambda limit or if the request for stationary torque if necessary with a hysteresis value by the fuel solution is less than the torque to be achieved by the air solution or if in the current operating mode the torque comparison is again satisfied, i.e. the signal B_schen is set to the state if at the same time the switching signal of the switching element 102 is put in the state. These conditions are represented in FIG. 2 in that the output signal of the AND combination 106 is inverted in the inverter 116 to be applied to an OR combination 118. Its output signal resets the flip- function flop 112. The other input of the OR combination 118 forms the output signal of the AND combination 120; in this, the information concerning a variation of the release signal B_schen is combined using the edge detection 122 and the state of the output signal of the timing stage 114. If the switching signal of the switching element 102 is set to the state and if at the same time there is a flank in the release signal, the flip-flop function 112 will be reset

in the initial state.

  Thanks to the above presentation, we first detect if we are in the presence of a lasting, lasting overshoot of the stationary Lambda limit for a high torque demand depending on the fuel solution. There is a high torque demand if the torque to be achieved by the fuel solution is greater than the desired torque to be achieved in the long term by the air solution. The torque request signal for the fuel solution takes account of functions which result in a stationary variation such as, for example, an idling control, while the functions which correspond only to dynamic interventions, such as an anti-shaking function, are not taken into account. So if the stationary Lambda limit is exceeded downwards for a high torque demand by the fuel solution, after a predetermined period, the setpoint torque is switched to the basis of the torque comparison used for release, to pass this torque from the desired torque value according to the air solution to the value to be achieved

by the fuel solution.

  To avoid a back-and-forth tilting of the comparison of torques, a torque hysteresis value MSOLLHYST at the combination point 130 is applied to the torque to be produced by the fuel solution. When a signal is produced at the output of the delay stage 114, the switching element 132 is switched to the position shown in broken lines, so that for the continuation of the comparison in 108, a larger value is used. This effectively prevents the signal toggling back and forth at the output of the floor

  114 and thus that of the comparison of couples.

  In the torque comparison, the desired stationary torque obtained in the manner presented is compared to the maximum theoretical torque possible in the current operating mode. If the first torque is greater than the maximum possible torque at the stationary limit, this operating mode will be prohibited. Otherwise, the operating mode will be authorized. Thus, the current operating mode is not automatically prohibited if the conditions mentioned above are met, but only if the stationary torque resulting from the fuel solution is outside the stationary operating limits. If the release signal Bschen is set, the selected current operating mode is carried out; on the contrary, if there is a ban, you must change the operating mode and switch to the other operating mode. Switching of the desired stationary torque is also done in this new operating mode. If the comparison of torques is still not satisfied, the last operating mode will not be authorized (in the present embodiment, it is the stratified mode). This avoids immediate switching to the old operating mode and thus a new ban resulting in a

  switching between operating modes.

  In conclusion, at least in the operating state described above, the reference torque is used which must actually be adjusted in this operating state to influence the state of the release signal.

Claims (6)

  1) Method for implementing a heat engine operating according to at least two operating modes, according to which an operating mode is selected and this operating mode will only be authorized if the torque requested from the heat engine can be achieved while respecting the limits of the air / fuel ratio for this operating mode, the maximum possible torque is determined at the limit of the air / fuel ratio for this operating mode and a signal to release the operating mode is reset if the requested torque cannot be achieved within limits, characterized in that   the requested torque is the setpoint torque that must actually be adjusted.   2) Method according to claim 1, characterized in that the requested torque is divided into a torque to be adjusted by the air supply and a setpoint torque to be adjusted by the fuel supply and / or the ignition angle.   3) Method according to claim 2, characterized in that the torque to be adjusted by the fuel supply and / or the ignition angle   is combined with the stationary component setpoint torque.   4) Method according to one of the preceding claims,   characterized in that in the event of an upward, permanent overshoot of the limit for a high torque demand, the setpoint torque to be effectively set in an operating mode is the setpoint torque of the solution   fuel with non-throttled operation of the engine.    ) Method according to claim 4, characterized in that outside of this operating state, the setpoint torque is   setpoint torque to be set by the air solution.   6) Method according to one of the preceding claims,   characterized in that when the release signal is reset, the switching of the operating mode.   7) Device for implementing a heat engine operating according to at least two operating modes, in which a mode of operation is chosen and this mode of operation is authorized if the torque requested from the heat engine can be achieved while respecting the limits of the air / fuel ratio for this operating mode, the maximum possible torque being determined at the limit of the air / fuel ratio for this operating mode to be compared with the requested torque and if the maximum possible torque is exceeded, the initial state the release signal of this operating mode, characterized in that the requested torque is the torque corresponding to the setpoint torque that it must actually settle.