FR2787512A1 - METHOD AND DEVICE FOR CONTROLLING AN INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

Method of controlling an engine equipped with a common rail system, according to which a pump supplies fuel to an accumulator. The values characterizing the pressure of fuel in the accumulator are entered and these values are used to control the fuel injection. Starting from at least two measured pressure values, a calculated pressure value used to control the fuel injection is defined

Description

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

  control device for an internal combustion engine no-

  especially for an engine fitted with a common rail system, according to which,

  - at least one pump supplies fuel in an accumulator-

tor,

  - the values characterizing the fuel pressure are entered

rant in the accumulator and,

  - these values are used to control the injection of fuel

  rant. Such a method and an internal combustion engine control device are already known according to document DE 195 48 278. This document describes a method and a device for regulating the pressure in a pressure accumulator.

  of a so-called common rail system (Common Rail system or system

  teme CR). Usually in such a common rail system, the duration of injector control depends on the amount of fuel to be injected and the pressure prevailing in the accumulator. For this it is necessary to detect the pressure in

  the accumulator synchronously at the speed of rotation.

  The pressure regulation is done according to a fixed time frame. For this, we detect synchronously in the

  time, the ramp pressure already detected syn-

  clock according to the speed of rotation.

  According to document DE 197 35 561 it is furthermore

  known to detect the pressure value in intervals

  fixed time. The command of the quantity of fuel to inject, gives precise quantities only if one knows

  fuel pressure at the start of injection. An impro-

  Cision of the pressure measurement can lead to a quantity defect and thus to a bad behavior of the emission

  gases from the internal combustion engine.

  Problem of the invention The object of the present invention is to develop a method and a device making it possible to reduce quantitative errors and thus improve the behavior at

  the emission of the internal combustion engine.

  -T Fi: To this end, the invention relates to a process of the type defined above, characterized in that starting from at

  minus two measured pressure values, a value is defined

  their calculated pressure used to control fuel injection. The invention also relates to a device for

  control of an internal combustion engine of the type defined above

  above characterized in that means starting from at

  minus two measured pressure values define a value

  their calculated pressure used to control the injection

fuel.

  Advantages of the invention The method and the device according to the invention make it possible to provide a pressure value which is very close to the effective value of the pressure at the start of the injection.

  According to advantageous features of the pro-

  assigned: * the calculated pressure value characterizes the fuel pressure in the accumulator at the start of injection, * the calculated pressure value is defined using a compensation function starting from the measured pressure values, * the pressure values measured between the previous injection and the current injection are entered, * the calculated pressure value, starting from the measured pressure values, predetermines a signal characterizing the

  start of injection and rotation speed.

  Drawings The present invention will be described below in more detail with the aid of an embodiment shown schematically in the accompanying drawings, in which: - Figure 1 is a block diagram of the device of the invention, - Figure 2 shows different timing diagrams, - Figure 3 shows a flow chart of the method of the invention.

  Description of the exemplary embodiments

  Figure 1 shows the elements necessary for understanding the invention according to one embodiment

  a fuel system for a gasoline engine

  internal bustion with high pressure injection. The system shown is usually called a common rail system (Common Rail system or CR system) and is given only for

example.

  The reference 100 designates a fuel tank

  rant. This is connected to an upstream feed pump 110. The upstream feed pump transfers the fuel by

  a line to a metering valve 120. The line connecting

  sound between the transfer pump and the metering valve 120 is

  connected by a low pressure limiting valve 145 to the

  power supply 100. The metering valve 120 is connected by a high pressure pump 125 to the ramp 130. The ramp is called an accumulator; this accumulator is connected by fuel lines to the various injectors 131. A

  pressure limiting valve 135 connects the rail 130 to the

  fuel supply 110. The metering valve

is controlled by a coil 136.

  The pipes between the outlet of the high pump

  pressure 125 and the inlet of the pressure limiting valve

  sion 135 are called high pressure zones. In this

  area, the fuel is under high pressure. The pressure re-

  interfering in the high pressure zone is detected using a sensor 140. The lines between the tank 100 and the

  high pressure pump 125 are called low pressure zone

  if we. Reference 150 designates an order. This

  supplies control signals A to the injectors 131 and

  requests the coil 136 of the metering valve 120. For this, the output signal P of the pressure sensor 140 and various signals supplied by other sensors 160 are used.

  than a speed sensor.

  The control 150 includes a filter 151 which receives the output signal PE from the pressure sensor 140. The filter 151 supplies the signals to a quantity calculation circuit 152 and a combination point 154. The second input of the combination point 154 receives the PS output signal of a

  circuit giving a set value 153. The circuit of

  their setpoint processes the output signal N of a speed sensor 160 as well as the output signal QK of the

quantity calculation circuit 152.

  The quantity calculation circuit provides the

  control glands A to the injectors; the value circuit of

  setpoint 153 provides the QK signal indicating the quantity to be in-

  ject that must be dosed. The output signal from the

  hoe 154 is applied to a pressure regulator 155 which

  in turn controls the coil 136 of the metering valve 120.

  This installation works as follows:

  boasts: the fuel in the tank is delivered by the pump

upstream 110.

  If the pressure in the low pressure zone has

  dyes an unacceptable level, the low limit valve

  pressure 145 opens and allows communication between the outlet

  tie of the upstream supply pump 110 and the tank 100.

  The high pressure pump 125 transfers the fuel

  rant from the low pressure zone to the high pressure zone.

  The high pressure pump 125 establishes a very high pressure.

  vee in ramp 130. Usually in mo-

  internal combustion engines with controlled ignition, the pressures are of the order of 30 to 200 bars and in the case of internal combustion engines with uncontrolled ignition, the pressures

  are of the order of 1000 to 2000 bars. The injectors 131 per-

  set to dose the fuel under high pressure to different

  the internal combustion engine cylinders.

  The sensor 140 detects the pressure in the boom or in the entire high pressure zone. The metering valve 120 controlled by a coil 136 makes it possible to regulate the pressure

  in the high pressure range. Depending on the voltage applied

  plied to the coil 136 or current passing through the coil 136, the metering valve 120 provides different flow rates to

the high pressure pump.

  To regulate the pressure P in the high zone

  pressure, other pressure relief devices can also be used

  -r -, 11; glage. These are alternatives to the metering valve 120,

  namely a supply pump 110, electric with adjustable flow rate or a pressure limiting valve 135 also controlled by a coil.

  The calculation of the control signals A as a function of the pressure P is done before each injection. This calculation is done according to the speed of rotation with an interval

  variable time. The distance between the calculations depends for-

  rotation speed. Calculation of the com-

  Control of the metering valve in the pressure regulator takes place at a fixed time rate. This cadence

  time is chosen so that the regulator can react im-

  medially at a variable set point PS and can be

  set this new value as quickly as possible

their instruction.

  The filter 151 processes the signal supplied by the cap-

  pressure sensor 140 and transmits this signal on the one hand to the circuit

  cooked quantity calculation 152 and on the other hand to the point of comparison 154 for the pressure regulation. The circuit of

  quantity calculation 152 calculates control signals A of-

  for injectors 131 as a function of pressure P and

  the amount of fuel to inject.

  The setpoint circuit 153 calculates a setpoint PS for the fuel pressure in the accumulator 130 from the various parameters of

  operation such as the speed (rotational speed

  tion) N of the internal combustion engine and the amount of

  fuel to inject QK. This PS setpoint is com-

  prepared at combination point 154 to the actual value PI four-

  negated by the filter 151. Based on this comparison, the pressure regulator 155 calculates the control signal for

  apply pressure control valve.

  The pressure prevailing in the accumulator varies very strongly. These variations result on the one hand from

  injection and secondly the establishment of the pres-

  if we. The pressure values required to calculate the quan-

  and / or pressure regulation are detected in fixed, fixed tempo intervals. This results in XTr -1T with large variations in the pressure values used for

  the calculation of quantities. Now, pressure values which will

  laugh strongly, lead to large variations in quantity.

  In addition, the pressure value obtained by entering the pressure differs greatly from the injection pressure. That

  results in a lack of precision of the injection.

  Figure 2 shows different signals as a function of time. Vertical marks designate impulses

  a tone wheel not shown. These impulses are pro-

  duce at defined angular intervals of the crankshaft

  or the camshaft. In the example of embodiment shown

  felt, the distance between two injections is divided into two increments; each time there is an incremental pulse at the injection level and an incremental pulse between

two injection pulses.

  The pressure curve P in the accumulator corresponds to the solid line. This is preferably a

  filtered signal. At the instant tE begins the injection. He re-

  the result is a very rapid drop in pressure. Then the pressure increases again. Immediately after the start of

  injection, the pressure is at PA level.

  The pressure measurement is made at the instants

  indicated by crosses t-n, t-n + l, ... tO which we know

  sit the pressure values P (m-n), P (m-n + l), .. P (m). The pressure is entered preferably at fixed time intervals chosen to have between two injections, at the

  minus two, and preferably three or more metric values

sure of pressure.

  Upon arrival of the incremental pulse located

  between the two injections, we initialize the calculation of

  control signals for the injectors, then the injection is carried out. This moment is marked with a small arrow

  vertical. The area in which the calculation of the

  control lines is characterized by a hatched surface.

  Thus, on the one hand, a signal is calculated which characterizes

  checks the start of the injection. It is a great size

  corresponding to the distance AB between the start of the injection identified by a zigzag arrow and the top dead center OT which occurs at time tOT. In addition, the duration AD of the command is defined. Both the duration of the AD command and

  the time interval AB are marked with a double arrow.

  The double arrow marks the distance K between top dead center TOT and the start of the calculation of the control signals. In the method according to the invention, to reduce the measurement error, the value of the pressure PA is evaluated at the start of the injection; this evaluation is made from several older measurement values P (mn), P (m-n + l), 10 .. (P (m). The measurement values are preferably entered with increasing pressure. means that the measurement values are started after the top dead center of the previous injection. Starting from at least two pressure measurements which occur in the interval between the previous injection and the current injection , i.e. the injection to be calculated, the value of the pressure PA is evaluated

  at the start of the injection to be calculated. Starting from at least

  their measured pressure, a calculated pressure value PA is defined which characterizes the fuel pressure in

  the accumulator at the start of the injection. The value of pres-

  PA output thus obtained is used to control the injection

fuel.

  For the evaluation, preferably a

  compensation function. Thus starting from different va-

  their measurements at different times, we define

  ment a compensation line against which the

  measured values differ only slightly.

  This line gives the relationship between pressure P and time t. Using this line, the value of the pressure PA at the instant tE of the injection can be defined. For this, it is necessary to know the instant tE. The instant tE follows from the distance K between the calculation of the control signals to

  the instant tO and the top dead center tOT. It is a va-

  their known angularity, because the calculation of the control signals begins with the arrival of an incremental pulse and the

  top dead center also coincides with an incremental pulse

mental.

  The distance between the two pulses increases

  corresponds to a known angular quantity according to which

  the crankshaft or camshaft rotate between the impulses

  incremental sions. Using the speed of rotation ins-

  tantane of the internal combustion engine, by calculation we transform this quantity into a duration indicating the distance separating the top dead center tOT and the instant tO at which

calculates the control signals.

  If the distance K is reduced by the value AB which designates the distance between the start of the injection tE and the neutral point tOT, then the distance K between the start of the calculation

  injection data and the start of injection is con-

  naked. Starting from the quantity K-AB and the equation of the line representing the pressure, the pressure PA is thus defined. It is particularly advantageous to use a

  other function in place of a compensation line, function

  tion which approaches the pressure curve so as not to leave

  ser only small deviations between the measured values and the values given by the function. It is particularly advantageous to use a function which is an approximation

  pressure changes even during injection.

  FIG. 3 explains the process according to the invention.

  tion using a flowchart. In a first step 300,

  the current value of pressure P (m) is detected.

  The following interrogation 310 checks whether the instant t0 has been reached. The instant t0 is reached, if the distance from the upper dead center is less than the value K.

  Alternatively, it can also be checked whether a pulse

cremental occurred.

  In the absence of this condition, in the step

  360, we replace the value of pressure P (m-1) by the value

  pressure (P), we replace the value of the pressure

  sion P (m-2) by the value of the pressure P (m-1) and we

  replaces the pressure value P (m-n) with the pressure value

sion P (m-n + l).

  If the interrogation 310 recognizes that one has arrived

  is at time tO, then in step 320 we calculate the de-

  1.F r purpose of the AB command for the next injection. Then in step 330, the instant tE at which the injection probably begins is defined, starting from the instant tOT at which the top dead center occurs, and the start of the command AB is defined. In the next step 340, the value of the pressure PA at the start of the injection is determined as a function F of the different pressure values P (m), P (m-1), P (mn), and the distance between the instant tO and the instant tE at which the injection takes place. This calculated pressure value PA10 is used in step 350 to calculate the control duration AD. This duration is predetermined according to the value of

  calculated pressure and other quantities K. This means that by applying this value PA, the control signal A is defined to control the injection of the quantity of fuel.

  In addition, this pressure value PA is used as an actual value by the pressure regulator 155.

Claims (1)

R E V E N D I C A T I ON S   1) Method of controlling an internal combustion engine no-   especially for an engine fitted with a common rail system, according to which, - at least one pump supplies fuel to an accumulator,   - the values characterizing the fuel pressure are entered rant in the accumulator and,   - these values are used to control the injection of fuel rant, characterized in that   starting from at least two measured pressure values,   ends a calculated pressure value used to command fuel injection.   ) Method according to one of the preceding claims,   characterized in that the calculated pressure value characterizes the pressure of the   fuel in the accumulator at the start of injection.   ) Method according to any one of claims 1 or 2,   characterized in that the calculated pressure value is defined using a compensation function on the basis of the pressure values measured.   ) Method according to any one of the preceding claims.   teeth, characterized in that the pressure values measured between injection are entered   previous and the current injection.   ) Method according to any one of the preceding claims. teeth, characterized in that   the calculated pressure value, starting from the pressure values   measured, predetermines a signal characterizing the start   of the injection and the speed of rotation.   777É II) Device for controlling an internal combustion engine, in particular an engine fitted with a common rail system, according to which * at least one pump transfers fuel from a tank,   * means enter characteristic pressure values   sant the fuel pressure in the accumulator and use them to control the fuel injection, characterized by: means which starting from at least two measured pressure values define a calculated pressure value used   to control fuel injection. -i, 1F V