EP1234964A1 - Method and apparatus for controlling the flow rate of a gas passing a throttle element - Google Patents

Abstract

Method involves generating a value for the weight of air flow across a butterfly valve (8) as a function of the amount pumped and with a transfer function (22) inverse to the transfer function of the inlet manifold (23) downstream of the valve. The position of the butterfly valve is controlled as a function of the value of the flow across the valve and external functional parameters.

Description

The present invention relates to methods and devices for controlling a gas flow (generally air) passing through a throttle device the position is adjusted by an actuator, from a flow rate setpoint pumped from cyclically by a receiver, a collecting volume being interposed between the throttling organ and the receiving organ.

The invention finds a particularly important application in internal combustion engine control systems having at least one combustion chamber of variable volume during a cycle, supplied with air at constant or variable pressure through a throttle whose position is controlled by an actuator, then through a manifold intake. The throttling organ is generally constituted by a butterfly rotary and the latter term will be used later. However, it should be attributed a general meaning and as applying to any throttling organ having a adjustable position.

We already know devices for controlling a mass air flow crossing a throttle valve from a flow rate instruction pumped downstream of the throttle valve, comprising a servo circuit which controls the position of the throttle in function of the flow setpoint and operating parameters such as air temperature and pressure. In the case of an engine, the average air flow pumped by the combustion chambers through the manifold is equal, in steady state, at the air flow which passes through the throttle member and the knowledge of the mass flow setpoint pumped (itself arising a torque setpoint set by the driver and the parameter value engine) allows the control circuit to determine the position to be given to the throttle member, the flow rate through the butterfly being equal to the set flow. But during transients, the collector introduced on the flow rate at the throttle valve low pass filtering which has not been taken into account so far. Existing devices therefore have the disadvantage of a large time constant, the longer the volume of space between the throttle valve and the flow setpoint location (entry of the receiving organ) is important.

The present invention aims in particular to provide a method and a device air flow control better than those previously known to requirements of the practice, in particular in that they significantly reduce the pilot time constant.

To this end, the invention notably proposes a method for controlling the air flow through a butterfly controlled by an actuator from a mass flow set point cyclically pumped through the throttle valve and a Downstream intake manifold according to claim 1.

This process is based on the fact that one can, without undue error, model the transfer function of a collector of the kind used in internal combustion engines as a first order function having as an inlet the mass flow of air passing through the butterfly and as an outlet the mass flow of pumped air, with a time constant which is a function itself pumped mass flow and cycle frequency (i.e. engine speed).

Qpompé désigne le débit à la sortie du collecteur et en entrée de l'organe récepteur,

Qpapillon désigne le débit traversant le papillon, et

t désigne le temps,

τ la constante de temps de la fonction de transfert associée au collecteur d'admission.

This transfer function can therefore be written as follows: Qpompé + τ (d Qpompé / dt) = Qpapillon or :

Qpumped designates the flow rate at the outlet of the collector and at the inlet of the receiver,

Qpapillon designates the flow through the butterfly, and

t denotes time,

τ the time constant of the transfer function associated with the intake manifold.

The time constant τ can be determined by a calibration prior and stored in a table with several entries.

The position given to the butterfly (opening angle in general) can be deduced at any time from Q butterfly by reading in a table taking into account temperature and pressure, supplied by sensors.

On certain internal combustion engines, recirculation of exhaust gas, which then adds to the mass flow through the throttle valve to constitute the pumped flow. This addition can be taken into account by modifying simply the command mode.

The invention also proposes a control device implementing the above method according to claim 6, as well as a system for internal combustion engine control in which the flow rate setpoint pumped is determined by a calculation unit from a torque setpoint supplied by a body controlled by the driver and possibly by additional torque calls due to the start-up of auxiliaries such as a air conditioning unit or a robotic gearbox in the case of a vehicle.

The implementation of the invention results, when applying a torque setpoint step, by the coming of the butterfly in a position beyond what it will take once the new permanent regime is established. This overshoot or "overshoot", the amplitude of which depends on the initial engine speed, does not mean that the pressure in the collector and has no drawbacks.

More generally, the invention proposes a device for controlling a throttle body controlled by an actuator and regulating a flow rate and a air pressure cyclically drawn through a function buffer volume known transfer device according to claim 5.

• à un circuit de recirculation des gaz d'échappement (éventuellement en même temps qu'à la commande de papillon),
• à un circuit de suralimentation par compresseur ou turbo-compresseur.

Apart from controlling a throttle valve, this device is particularly applicable:

• an exhaust gas recirculation circuit (possibly at the same time as the throttle valve control),
• to a supercharging circuit by compressor or turbo-compressor.

It is not necessary that the transfer function are first order.

• la figure 1 est un schéma destiné à faire apparaítre le principe du pilotage d'un organe d'étranglement placé en amont d'un volume tampon ;
• la figure 2 est un diagramme montrant l'évolution du débit pompé lors d'une augmentation brutale du débit papillon ;
• la figure 3, similaire à la figure 2, montre la variation à faire subir au débit papillon pour obtenir une augmentation rapide d'un échelon du débit pompé ;
• la figure 4 est un synoptique représentant, sous forme de blocs successifs, les opérations qui interviennent dans le pilotage du débit massique d'air traversant un papillon ;
• la figure 5 est un schéma montrant les éléments essentiels du circuit pneumatique d'alimentation des chambres de combustion d'un moteur à injection.

The above characteristics as well as others will appear better on reading the following description of a particular embodiment given by way of nonlimiting example. The description refers to the accompanying drawings, in which:

• Figure 1 is a diagram for showing the principle of piloting a throttling member placed upstream of a buffer volume;
• Figure 2 is a diagram showing the evolution of the flow pumped during a sudden increase in the butterfly flow;
• Figure 3, similar to Figure 2, shows the variation to be subjected to the butterfly flow to obtain a rapid increase of one step of the pumped flow;
• Figure 4 is a block diagram representing, in the form of successive blocks, the operations involved in controlling the mass flow of air passing through a butterfly;
• FIG. 5 is a diagram showing the essential elements of the pneumatic circuit supplying the combustion chambers of an injection engine.

The diagram in FIG. 1 indicates the transfer function of a buffer volume 23 placed downstream of a throttle member 8. As will be seen in more detail below, this transfer function, if it is linear, can be written in Laplace notation: 1 / (1 + τp)

This transfer function causes, in the event of rapid opening of the throttle resulting in a flow step at the throttle level, by a progressive increase in the pumped flow (FIG. 2). On the contrary, it is possible to obtain a flow step pumped very quickly, as indicated in dashes in FIG. 3, by an excessive increase in the butterfly flow (curve in solid lines). For this, the butterfly must be ordered by implementing a transfer function compensating for that of the buffer volume, of the form: 1 + τ.p K / (1 + τf.p)

The diagram in FIG. 4 shows the operations and the loops of regulation involved in controlling the opening angle of the throttle valve 8 of an internal combustion engine 9, in response to a request from torque produced by the driver's action on an accelerator pedal and by variations in the torque required by auxiliaries using power to the engine. Most of the blocks shown in Figure 1 can be constituted by wired circuits or by programs which in this case can be executed either by a specific microprocessor or by the engine control computer provided on current vehicles. The calculations are performed in digital form, which involves sampling and store the input data. On current engines, a period 0.01 s sampling rate was found to be satisfactory.

Block 10 of Figure 4 represents the calculation of a digital signal indicating the average torque indicated CMI, which must be supplied by engine 9 and corresponds to an average air flow determined in steady state. The data of input of block 10 are the position of the pedal, supplied on an input 12 and representative of the setpoint torque that the driver wishes to apply to wheels, the engine speed N applied to an input 13 and giving the frequency debit calls by the rooms, and finally an entry indicating the call of torque possibly required by auxiliaries. When the sensors are analog, digital to analog converters not shown are provided. The output signal from block 10, representative of the average torque indicated CMI, is translated by a block 14 into a flow rate setpoint Qpompé, which will called Qpc. A regulation loop includes a subtractor 16 which receives the setpoint signal Qpc on an input and a signal indicating the pumped flow estimated real Qpr on the other entry. The error ε is applied, as well as Qpc, to a filter 18, generally of the PID type. The output of this filter constitutes a signal flow objective pumped Qpo. But assimilate Qpo to a flow instruction butterfly neglects the transfer function due to the dynamic behavior of air in the collector. Block 19 estimates the actual pumped flow mainly from temperature data T, pressure P and speed N of rotation of the engine.

In a motor control system according to the invention, the signal representative of Qpo is not used directly to calculate a value of setpoint αc of the throttle opening angle in a circuit 20 taking into counts the characteristic curve of the butterfly and the temperature T and the pressure F gas upstream of the throttle valve. The signal Qpo is processed by a block 22 which applies a function inverse to the estimated transfer function of the collector 23 (figure 2), as will be seen below so as to provide an outlet a Qpapo signal representative of a throttle flow objective.

The butterfly 8 is controlled, in a conventional manner, by a loop of regulation comprising a subtractor 24 which receives on an input the opening of setpoint αc and on the other input a signal representative of the actual opening current αr and blocks 26 for controlling the actuator 28 of the throttle valve and 27 for supply of a signal αr representative of the opening angle.

The correction introduced by block 22 is determined from a behavior model of the collector 23 of the form given in (1). It can be written, as a Laplace transform: (Qpompé / Qpap) = K / 1 + τ.p)

The correction introduced consists in applying, to the signal representative of Qpompé, a reverse transfer function. This operation amounts to a high pass filtering of type 1 + τ.tp / K, where τ and K are coefficients which depend on fixed characteristics of the engine (volume of the manifold, number of combustion chambers, ...) and of the motor speed. This filtering also results in amplification of noise. To avoid this and to cut the weakest time constants of the model, which would be incompatible with the sampling period which is chosen at a value low enough to take into account Shannon's theorem, it is desirable to add filtering low pass, having a time constant τf much shorter than the time constant of the collector (at least an order of magnitude). We then have: (Qpap / Qpompé) = (1+ τp) / (K / 1 + τf.p)

It will be the value of the shortest time constant which will then set a maximum duration for the sampling period.

N est la vitesse du moteur, en nombre de tours par minute, par exemple,

K1 est proportionnel au rapport entre le nombre de tours par cycle et le nombre de chambres,

K2 est le rapport entre le volume du collecteur et le volume d'une chambre,

K3 est représentatif des rendements de remplissage, et dépend de la température et de la vitesse,

τ peut, sur un modèle donné de moteur, être mesuré une fois pour toutes aux diverses allures de fonctionnement susceptibles d'être rencontrées, puis les valeurs sont mémorisées, dans une table mise en oeuvre lors de l'opération figurée dans le bloc 22.

The application of reverse high pass filtering of the transfer function of the collector implies having the values of τ and K under the various operating conditions of the engine. It will generally suffice to memorize a table of values of τ as a function of the speed of rotation of the motor and of the temperature of the air in the manifold. Indeed, τ can generally be written in the form: τ = K1.K2.K3.1 / N or :

N is the speed of the motor, in number of revolutions per minute, for example,

K1 is proportional to the ratio between the number of turns per cycle and the number of rooms,

K2 is the ratio between the volume of the collector and the volume of a room,

K3 is representative of the filling yields, and depends on the temperature and the speed,

τ can, on a given model of engine, be measured once and for all at the various operating speeds likely to be encountered, then the values are memorized, in a table implemented during the operation shown in block 22.

The process whose steps have been described above is still applicable when the torque requested by the driver and materialized by the signal on input 12 must be juxtaposed with a torque setpoint additional requested by an auxiliary, for example by a box of automatic or robotic speed, by a speed or distance regulator, the braking system or an engine performance limiter. In this case, for make the action caused by a torque step less brutal, the pumped flow from the box is translated into butterfly flow by a filter phase advance also reversing the dynamics of the collector.

Finally, the process can be modified to take into account an exhaust gas recirculation. In this case, the flow admitted to the combustion chambers, that is to say the pumped flow, depends on both the butterfly flow and the recirculation flow. In this case, the assumption that the above regulation is based, which is that the air mass in the manifold M is related to the flow rates by: Qpap = Qpompé + (dM / dt) is replaced by: Qpap + QEGR = Qpompé + (dM / dt) where QEGR is the part of the exhaust gas recirculation flow consisting of air.

In this case, the unique equation connecting Qpap to Qpompé is replaced by a system of two equations, one of which involves the time constant of recirculation system, which simply means applying two filters different high pass, corresponding to different time constants, signals representative of the butterfly flow and the recirculation flow.

Claims (7)

Method for controlling the flow of air passing through a throttle valve controlled by an actuator, from a mass flow instruction, pumped cyclically, through the throttle valve (8) and an intake manifold (23) placed downstream , of the throttle valve, according to which a set point of mass air flow through the throttle is generated from the set point of pumped flow and of a transfer function (22) opposite to the transfer function of the manifold and the throttle position as a function of said flow rate setpoint through the throttle valve and of external operating parameters measured or stored, the reverse transfer function being a filtering of the form: (1 + τ.p) / [K / (1 + τf.p)] where τ and K are coefficients depending on the cycle frequency and the temperature of the gas in the collector and where τf is a time constant less than at least an order of magnitude than the constant τ. Method according to claim 1, characterized in that an additional requested instruction is added to the pumped flow instruction, representative of a torque demand introduced by a driver of an internal combustion engine supplied by the pumped air. by an engine auxiliary which is translated into throttle flow by a phase advance filter. Method according to claim 2, characterized in that account is taken, in the pumped flow admitted to the combustion chambers, of a recirculation flow. Method according to claim 3, characterized in that a low-pass filtering is also applied to compensate for the dynamics of the recirculation circuit. Device for controlling a throttle member controlled by an actuator and regulating a flow rate and a pressure of air aspirated cyclically through a buffer volume of known transfer function, characterized by means for memorizing a reverse transfer function the buffer volume transfer function, means for generating a mass air flow setpoint through the throttle member from the pumped flow setpoint and a state control circuit (26) ( α) of the throttle member as a function of the said mass flow setpoint through the member and of external operating parameters measured or stored. Device for controlling an air flow passing through a throttle valve (8) controlled by an actuator (28), from a mass flow set point pumped cyclically through the throttle valve and an intake manifold placed downstream of the throttle valve, characterized by means for memorizing a reverse transfer function of the transfer function of the collector, means for generating a mass air flow setpoint through the butterfly from the pumped flow setpoint and a circuit ( 26) for controlling the position (α) of the butterfly as a function of said mass flow setpoint through the butterfly and of external operating parameters measured or stored, said reverse transfer function being a filtering of the form: (1 + τ.p) / [K / (1 + τf.p)] where τ and K are coefficients depending on the cycle frequency and the temperature of the gas in the collector and where τf is a time constant less than at least an order of magnitude than the constant τ. Device according to Claim 5, characterized in that the said parameters are the temperature and the pressure of the intake air as well as the pressure upstream of the butterfly valve.

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