FR2837527A1 - METHOD AND ASSEMBLY FOR PRESSURE ADJUSTMENT OF A SUPERCHARGED ENGINE - Google Patents

Abstract

We protect against overloads of a turbocharger (3) of a supercharged engine (1) by incorporating into the conventional electronic control unit (2) a module for limiting the boost pressure setpoint (15), which is sensitive to the air flow, the temperature of the air entering the compressor and the atmospheric pressure measured (9, 14, 13). The choice of these parameters makes it possible to avoid situations of excessive compressor or pumping speeds. The boost setpoint calculated according to the current state of the engine is only overridden by the limitation when it becomes greater than it. It becomes possible to safely choose higher setpoint cards, which remain independent of air pressure and temperature. The invention applies to diesel engines or to other internal combustion engines.

Description

B 14010 AP

  ENGINE PRESSURE ADJUSTMENT METHOD AND ASSEMBLY

SUPERCHARGED

DESCRIPTION

  The subject of this invention is a method for adjusting the pressure of a supercharged motor of an automobile, in particular in order to protect the turbocharger from overloading, and it applies first to diesel engines, but without the engines gasoline are excluded from its application. An assembly consisting of the engine, its supercharging system and the pressure adjustment means is also part of

the invention.

  The technical field to which the invention relates is the control-command of an automobile internal combustion engine by means of a set of sensors and actuators as well as a calculator called UCE (electronic control unit) which contains all the control-command laws in the form of software and engine characterization parameters. In addition, the engine being supercharged, it is equipped with a turbocharger whose purpose is: to increase the amount of air admitted into the cylinders. Its turbine is placed at the exit of the exhaust manifold and is driven by the exhaust gases. The power supplied by the exhaust gases to the turbine can be adjusted by installing a relief valve, or fins which modify the entry section in the turtine. Its compressor, coaxial with the turbine, compresses the air which enters the intake manifold. The device

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  supercharging is controlled by the ECU according to various operating parameters; it acts on an actuator which controls the degree of opening of the relief valve or the fins. Usually, the ECU calculates an air pressure setpoint in the intake manifold leading to the engine while measuring the pressure that is actually reached there; the purpose of the command exerted on the actuator is to

  reduce the pressure measured to the pressure setpoint.

  The ECU receives information about the engine's operating condition, which is often its engine speed (rotational speed) and fuel crime, although fuel and air crime information may also be used. It deduces therefrom a gross boost pressure setpoint value by means of a card, that is to say values of a multi-dimensional function which has been recorded before. This raw value is then corrected according to the atmospheric pressure and the temperature of the air entering the compressor in order to determine a corrected value of the boost pressure setpoint, which is used to control the turbocharger. The boost setting is defined in function of the engine's need for air for stabilized operations and allows the engine to be given the air flow allowing the

better combustion.

  However, the manufacturer must ensure that the pressure setpoint does not overload the compressor. However with the increase in the performance of supercharged engines, the pressures of

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  overeating also increase. It therefore becomes important to precisely control the turbochargers, the areas of use of which are now close to overloads which would damage the compressor. In addition, faults in the supercharging circuit are liable to disturb the control, the routine of the ECU being liable to place the turbocharger in the overload regions: it would therefore be useful to be able to detect the appearance of such faults. Finally, we would like the control process to operate in as little degraded mode as possible when a fault has

been detected.

  A situation to avoid is that of pumping, which consists of an inversion of the air flow through the compressor for low flow rates. It is also necessary to avoid overspeeds of rotation of the turbocharger shaft. The pressure setpoint must therefore be limited. Figure 1 shows the operating range of the air dehit Wc * and the compression ratio through the compressor. We have shown on the diagram some curves N1 to N6 giving the values of these compressor service parameters: according to its speed of rotation, speed N6 being the maximum speed allowed and the overspeed zone V being at the top and to the right of its curve, that is to say on the side of compression rates and high bit rates; the curves N stop to the left at a limit X beyond which (on the side of the low crimes) is the pumping zone P. The invention originates from the observation - that the usual mode of calculation of the setpoint pressure

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  was not excellent since it did not involve the quantities which made it possible to detect an overload of the compressor, which made it necessary to limit as a precaution the performances which were required of it for the supercharging. An improved method is therefore proposed here, in which the requirements for ensuring the best combustion in the engine and for respecting the turbocharger are both respected in the calculation of the boost pressure setpoint, so that the maintenance of the compressor in the proper operating range depends on an estimate based on the operating parameters of the compressor itself, and no longer only on a setting made once and for all by means of a map according to the parameters of

engine operation.

  The invention also makes it possible to take account of faults in the supercharging circuit in order to amend the pressure setpoint in order to remain within the suitable operating range of the turbocharger, at the cost of a dogradation of the engine performances, which

  is not possible with the usual ordering process.

  These faults can be detected and reported to the driver. An additional object of the invention is to accomplish these improvements without installing additional sensors which would have the effect of increasing the cost of the vehicle, and in particular without directly measuring the compression ratio and the speed of the compressor. The only necessary adjustments 13994fJCI are then made in the OCE itself in the form of additional software functions. In its most general form, the invention relates to a method for adjusting the pressure of a supercharged engine, in particular in order to protect overloads a compressor placed on an air flow towards the motor, comprising a calculation of a pressure setpoint, characterized in that it comprises an estimate of a pressure limit by means of a measurement of dehit of air passing through the compressor and an extreme compression rate authorized for this air deflection, and a reduction of the pressure setpoint at the pressure limit if said limit was less than

said instruction.

  The invention also relates to an assembly comprising an automobile engine, a system for boosting the engine and means for adjusting the supercharging, the system comprising an air flow duct leading to the engine. and a compressor, and the adjustment means comprising means for calculating a pressure setpoint to be established in the duct between the compressor and the motor, and an air flow sensor in the duct, characterized in that that the adjustment means comprise a means of calculating a compression ratio of the air through the compressor, a means of determining a pressure limit as a function of the air gap and the compression ratio , and a means of correcting the setpoint

  pressure according to the pressure limit.

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  It is advantageous, in accordance with the above remark, that only the air gap, the

  air pressure and temperature are measured.

  The detection of flow faults may include detecting air leaks from the flow between the compressor and the motor, or a

  detection of pumping in the compressor.

  The invention will now be described by means of the following figures: FIG. 1 is a diagram of the operating field of a turbocharger; - Figure 2 is a diagram of a supercharged engine; - Figure 3 is a UCE diagram; - Figure 4 illustrates the operation of the pressure setpoint limitation module; - Figures 5 and 6 illustrate two anomalies detection circuits; - and Figure 7 illustrates another circuit

detection.

  We discuss Figure 2 o the engine, the ECU and the turbocharger have the references 1, 2 and 3, the compressor and the turbine having the references 4 and 5. The air supply circuit of the engine comprises a manifold intake 6 and an exhaust manifold 7; this one successively carries an air filter 8 and a flow meter 9 upstream of the compressor 4, then a heat exchanger 10, an intake flap 11 and a valve 12 between the - compressor 4 and the engine 1; he goes through the l

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  compressor 4 while the exhaust manifold 7 passes through the turbine 5. Finally, the ECU 2 is informed by an atmospheric pressure sensor 13, an air temperature sensor 29 at the inlet of the compressor and by the delimiter 9. It essentially consists of a pressure setpoint calculation module 14, a pressure setpoint limitation module 15 and a boost pressure regulation module 16. It is the latter which adjusts the operation of the turbocharger 3 by controlling an actuator 17 generally consisting of a proportional control valve whose displacement causes

  the adjustment member 18 of the turbocharger 3, which is.

  as already mentioned, most often a group of fins modifying the inlet section in the turbine 5. The equation module 16 receives the pressure value in the intake manifold 6 downstream of the compressor 4, that a sensor 19 measures and which we note here Pcol, to perform the equation. The modules 14 and 16 are known, unlike the module for limiting the pressure setpoint 15 which is the subject of the invention and will now be described in detail; However, it should be noted that it is he that the atmospheric pressure and air temperature sensors 13 and 29, as well as the flow meter 9, provide information, instead of the setpoint calculation module 14, in disagreement with the traditional design. This means that the boost pressure setpoint given by the module 14 will be independent of the

  temperature of atmospheric air pressure.

l

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  FIG. 3 is a more detailed view of the ECU 2 and of the modules 14, 15 and 16. For the module for calculating the pressure setpoint 14, it contains a setpoint card 20, informed by an engine speed sensor 30 and a fuel flow sensor 31, and the output signal is transmitted to the setpoint limitation module 15, which will now be described in connection with FIG. 4 detailing a cycle of its operation. The first step E1 is a calculation of the pressure Plc at the inlet of the compressor 4,

  which is given by the subtraction Plc = PaLmo - APcF.

  The atmospheric pressure PaLmo is given by the sensor 13, and the pressure PcF is actually a pressure drop in the air filter 8, which can be given by a card 21 as a function of the air flow rate. The second step E2 is a caloul, in an element 22 of the circuit, of the corrected delict (mass) passing through the compressor 4 Wc * and which is calculated from the temperature Tlc, the pressure Plc and the volumetric deLit Q measured by the sensors 8, 13 and 29 in front of the compressor 4, and of the engine speed Nmot. The coefficient Cnorm is a scaling coefficient, ega-l at 0.1144 in this case, and Tref is a reference temperature at which the compressor operating curves are obtained. The temperatures are in C, the pressures in hpa, Nmot in rpm, Q in mg / cp or milligram per stroke (fuel injection in the

motor) and Wc * in kg / h.

  The third step E3 is a calaul of the maximum authorized compression rate ncmaX, taken from a map

23 depending on the Wc * delIT.

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  The third step E3 is a calaul of the maximum authorized compression rate cmax, taken from a map

23 depending on the Wc * delIT.

  The fourth step E4 is a caleul of the maximum permissible pressure ion at the outlet of the compressor

  given by the multiplication P2 cmax = cmax x Plc.

  The fifth step E5 is a calculation of the maximum pressure setpoint, which is given by the subtraction Pcolmax = P2cmax - APCRAS, APCRAS being a pressure drop in the exchanger 10, taken from a card 24 as a function of the air flow Q Finally, a sixth step E6 of the cycle is carried out in a comparator 25 which selects the minimum value between Pcolmax calculated previously and the value P setpoint taken from the setpoint calaul module 14. It is this minimum value which is transmitted to the regulation module 16. The elements ensuring the subtraction and multiplication in steps E1, E4 and E5 bear the references 26, 27 and 28

respectively in Figure 3.

  The request module 16 conventionally comprises derivative servo cards 50, and: proportional and integral 51 of which the result of the first arrives directly at an output adder 52 while that of the other arrives at an intermediate adder 53 which adds the result drawn from a pre-positioning card 54 before transmitting it to a saturator 55 whose effect is to prevent an excessive value from being produced by the proportional and integral servo card 51. The result then arrives to the adder of

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  output 52, which calculates a sum which is the signal of

  command transmitted to the actuator 17.

  The pre-positioning card 54 is sensitive to the engine speed and to the dehit of fuel, just like the card 20. Finally, the servo cards 50 and 51 are supplied with a signal equal to the difference between the output of the module of limitation 15 (the minimum of setpoint and Pcolmax) and the pressure signal Pcol measured in the intake manifold 6 by the sensor 19. We will not extend further on this module.

  requisition 16, which is entirely apparent in the known art.

  It has already been mentioned that an important advantage of the pressure setpoint limitation proposed by the invention is that the designer of the ECU 2 no longer has to take into account the risks of excessive speed or of soaking of the turbocharger 3 by making calibration, which alleviates his work. Anomalies in the supercharging circuit could facilitate the appearance of these compressor overloads, but the setpoint pressure limitation process avoids them without any particular measure and leads: in fact then the engine control to a dograded operating mode, although only optimal since it is close to the authorized limits. It may however be useful to detect these abnormal conditions in order to warn the

  driver of the interest of a subsequent repair.

  The devices proposed to accomplish this detection represent other aspects of the invention which will be

described below.

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  A main damage is thus constituted by an air leak in the intake manifold downstream of the compressor 4, which would have the effect of imposing a higher speed of rotation on the turbocharger to obtain the same compression ratio and would increase therefore the risk of overspeed. The detection circuit, illustrated in FIG. 5, operates in such a way as to detect these leaks when the following conditions will be achieved simultaneously: - the boost pressure setpoint is effectively limited by the module, - the atmospheric pressure is greater than a threshold , - and the air delIT at compressor 4 is higher than a threshold, which is a function of the rate of

compression measured.

  There is thus a battery of three comparators 35, 36 and 37 which respectively compare the boost pressure setpoint and the boost pressure setpoint limitation originating from modules 14 and 15, the atmospheric pressure originating from sensor 13 and a threshold present in a memory 38, and the air flow Wc * originating from the element 22 at a threshold given by a card 39 according to the indication coming from a circuit situated further upstream and comprising an adder 40 o, the pressures of Pcol supercharging measured by the sensor 19 and the pressure drop at the APcRAS exchanger given by the card 24, the result

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  being divided by the value P1C in a divider 41. The outputs of the three comparators 35, 36 and 37 are combined in an AND gate 42, the result of which is therefore positive, in the event of air leakage, only when the outputs of the three comparators are all equal to 1. Other damage will have the effect of reducing the detit of air passing through the compressor, in particular if an accident appears in the circuit downstream of this compressor. It is then a pumping that the turbocharger 3 would risk undergoing. However, the application of the invention will limit the boost pressure setpoint since the air flow will be reduced. But here too a detection circuit can be added to the device. It is proposed to detect pumping when the following conditions will be carried out simultaneously: - the boost pressure is greater than the limited pressure setpoint (from module 15), - and the air flow at compressor 4 is below a threshold, which is a function of the rate of

  estimated compression in compressor 4.

  The circuit will therefore include a comparator 43 supplied by the measured boost pressure Pcl, originating from the sensor 19, and by the pressure setpoint limitation Pcolmax originating from the module 15, and another comparator 44 supplied by the corrected air fault Wc * of element 22 by a card 45 similar to card 39 and sensitive to the same magnitude as this one, calculated by an adder 46 and a divider 47 similar to the corresponding elements 40 and 41

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  encountered previously and fed in the same way.

  However, the thresholds given by cards 39 and 45 may be different. The outputs of the comparators 43 and 44 are connected to an AND gate 48 which emits a positive signal, representative of a dip detection, if the comparators 43 and 44 both give

a result equal to 1.

  Another improvement that can still be made to the invention relates to the calculation of the speed of rotation of the turbocharger 3, in order to be able to confirm the good performance of the equation. One can incorporate a circuit such as that of FIG. 7, which uses the corrected deLit Wc * through the compressor 4, as well as the compression ratio, which is indicated on a card 49 which reproduces the diagram of FIG. 1 and gives a gross speed NTC of rotation of compressor 4 before supplying it to a calculation module which, depending on the temperature Tlc, performs the calaul of the speed of rotation rcelle NTC * of the turbacompressor according to the estimate:

  NTC * = NTC x, / ([lc + 273.5) / 7'ref.

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Claims (11)

  1) Method for adjusting the pressure of a supercharged automobile engine, in particular in order to protect from overloads a compressor (4) placed on an air flow towards the engine (1), comprising a calaul of a pressure setpoint (Setpoint), characterized in that it comprises an estimate of a pressure limit (Pcolmax) by means of a measurement of air flow (Q) passing through the compressor and of an extreme compression rate (cmax) authorized for this air gap, and a reduction of the pressure setpoint to the pressure limit if said limit is less than said instruction.   2) A method of adjusting the pressure of a supercharged engine according to claim 2, characterized in that the calculation of the pressure setpoint is carried out independently of temperatures or air pressures.   3) A method of adjusting the pressure of a supercharged engine according to claim 2, characterized in that it comprises a correction (wc *) of the measured air pressure (Q) by means of measurements of a pressure and an air temperature upstream of compressor.   4) A method of adjusting the pressure of a supercharged engine according to claim 3, characterized in that only the air flow, the pressure and the air temperature are measured to estimate the pressure limit. B 13994 / JCI   ) Method for adjusting the pressure of a supercharged engine according to claim 3, characterized in that the air pressure is obtained by subtracting a pressure drop (APCF) through an inlet filter (8) in the flow, estimated according to the measured air DELIT, of a pressure of atmospheric air (PaLmo).   6) Method for adjusting the pressure of a supercharged engine according to any of the   claims 1 to 5, characterized in that the limit   pressure (Pcolmax) is obtained by subtracting a pressure drop (APcRAS) through a heat exchanger, placed on the flow between the compressor and the engine, estimated according to the measured air flow,   a pressure (Pcmax) calculated downstream of the compressor.   7) Method for adjusting the pressure of a supercharged engine according to any one of   Claims 1 to 6, characterized in that it comprises   detection of air leaks out of the flow between the compressor and the engine.   8) A method of adjusting the pressure of a supercharged engine according to claim 7, characterized in that the detection of air leaks is positive when the pressure setpoint is greater than the pressure limit (35), a pressure d the atmospheric air is above a threshold (36) and the   air flow is greater than a threshold (37).   9) Method for adjusting the pressure of a supercharged engine according to any one of   Claims 1 to 8, characterized in that it comprises   - detection of pumping in the compressor. B 13994 / JCI   ) A method for adjusting the pressure of a supercharged engine according to claim 9, characterized in that the pumping detection is positive when a measured supercharging pressure is greater than the pressure limit (43) and when the air gap is below a threshold estimated based on   an estimated compression ratio of the compressor.   11) Assembly comprising an automobile engine, a system for boosting the engine and means for adjusting the boost, the system comprising an air flow duct leading to the engine and a compressor, and the means for adjusting comprising means for calculating a pressure set point to be established in the duct between the compressor and the motor, and an air-flow sensor in the duct, characterized in that the adjusting means comprise a calaul means of a compression ratio of the air through the compressor, a means of determining a pressure limit as a function of the air flow rate and the compression ratio, and a means of correcting the pressure setpoint according to the pressure limit.   12) An assembly according to claim 11, characterized in that the adjustment means comprise means for detecting air leaks out of the duct and pumping the motor according to flow measurements and air pressure.   13) Assembly according to any one of   claims 11 or 12 characterized in that it   includes means for estimating (49, 50) the speed of rotation of the turbocharger.