Method for triggering the controlling elements of an internal combustion engine

There are a number of controlling elements of an internal combustion engine which have an influence on the charge of the cylinders. For each controlling element, a triggering instant is determined that is adapted to its individual reaction time, so that all the controlling elements simultaneously deploy their action influencing the charge. In this manner, a desired charge is attained at a defined instant, thus permitting a harmonious adjustment of the charge to other operating parameters. This optimizes the driving properties, the performance and the fuel consumption of the internal combustion engine.

BACKGROUND INFORMATION
 In an internal combustion engine, the charge of the cylinders is mainly
 controlled by way of the throttle valve in the induction pipe. However,
 there are a number of other controlling elements which have an influence
 on the charge, as well. In particular, they are controlling elements which
 are used to improve the driving properties, or to ensure operation of the
 internal combustion engine which is optimized from the standpoint of
 performance and fuel consumption. Belonging to these controlling elements
 are, e.g., an exhaust-gas recirculation valve, a device for changing the
 geometry of the induction pipe, a device for changing the position of the
 camshaft, and a device for the adjustment of swirl valves in the intake
 ports of the cylinders. The influences of all these controlling elements
 on the charge are very different. The result is that, in response to a
 change in the engine load, a change takes place in the charge which is not
 in harmony with other operating parameters of the engine such as the
 ignition-advance angle, the start of injection or the injection quantity.
 This phenomenon leads to a deterioration in drivability, and also does not
 allow operation of the engine which is optimized from the standpoint of
 performance and consumption.
 Therefore, an object of the present invention is to provide a method by
 which the driving properties are improved and which permits an operation
 of the engine which is optimized from the standpoint of performance and
 fuel consumption.
 SUMMARY OF THE INVENTION
 According to the present invention, for each controlling element, a
 triggering instant is determined which is adapted to its individual
 reaction time, so that all controlling elements simultaneously deploy
 their action influencing the charge. This measure makes it possible to
 achieve a desired charge at a defined point of time, so that a clear time
 relation to the change of other operating parameters can be attained.
 The triggering instant for each controlling element can be determined as a
 function of the engine speed. The controlling element can be triggered
 when a specific lead speed is reached which is before a setpoint speed at
 which the charge must have reached its setpoint value. To that end, a
 setpoint speed is ascertained corresponding to the driver's input, a speed
 gradient is ascertained from the instantaneous speed and the setpoint
 speed, and the individual lead speed for each controlling element is
 derived from the setpoint speed and the speed gradient, taking into
 account the reaction time of the controlling element.

DETAILED DESCRIPTION
 An internal combustion engine 1, having an induction pipe 2 and an exhaust
 duct 3, is shown schematically in FIG. 1. An exhaust-gas recirculation
 duct 4 leads from exhaust duct 3 to induction pipe 2. An exhaust-gas
 recirculation valve 5 is inserted in exhaust-gas recirculation duct 4 as a
 controlling element for adjusting the exhaust-gas recirculation rate. As
 German Patent No. 196 256 88 describes, such an exhaust-gas recirculation
 is used to increase performance and to improve the exhaust-gas emission of
 an engine.
 Located in induction pipe 2 is a throttle valve 6 whose opening is
 controllable by a controlling element 7. Block 8 indicates the arrangement
 of a controlling element for changing the geometry of the induction pipe,
 and block 9 symbolizes a device for adjusting the camshaft. As German
 Patent No. 44 35 741 describes, adjusting devices for the induction-pipe
 geometry and for the camshaft setting, respectively, are used to increase
 engine output, to reduce fuel consumption and to improve exhaust-gas
 emission.
 Block 10 indicates a device for the adjustment of swirl valves arranged in
 the individual intake ports of the cylinders. Such swirl valves are
 usually provided in internal combustion engines with direct fuel injection
 in order to attain a certain mixture turbulence in the combustion chambers
 of the individual cylinders.
 All the indicated controlling elements 5, 7, 8, 9, 10 have an influence on
 the charge of the individual cylinders. However, they have very different
 reaction times, so that the charge changes produced by the individual
 controlling elements become effective at different times. Without the
 method yet to be described in detail with reference to FIG. 2, there is no
 defined point of time at which a desired setpoint charge of the cylinders
 is reached. An engine control unit 11 triggers each of the indicated
 controlling elements 5, 7, 8, 9, 10 as a function of time, taking into
 account the reaction times of the individual controlling elements, so that
 the charge reaches its setpoint value at a quite specific point of time.
 Exhaust-gas recirculation valve 5 receives control signal sag, controlling
 element 7 for throttle valve 6 receives control signal skd, controlling
 element 8 for the induction pipe geometry receives control signal SST,
 controlling element 9 for the camshaft adjustment receives control signal
 snw, and controlling element 10 for the swirl valves receives control
 signal sdr. In addition, engine speed n sensed by an engine speed sensor
 12, and position fp of gas pedal 13 representing the driver's input are
 supplied to engine control unit 11.
 In order to implement a timed, individual triggering of the various
 controlling elements to achieve a change in the charge at a defined
 instant, the following method, presented in FIG. 2, is performed in engine
 control unit 11.
 In a first method step 20, the driver's input fg is detected and a setpoint
 speed ns is ascertained therefrom. A specific setpoint speed ns can be
 allocated to each driver input, i.e., to each position of the gas pedal.
 Setpoint speed ns is preferably derived from a family of characteristics
 which is a function of gas-pedal position fp.
 In second method step 21, a speed gradient n is ascertained from the
 prevailing speed, i.e., instantaneous speed n, and from setpoint speed ns.
 According to the third method step 22, a lead speed nv is derived from
 setpoint speed ns and from speed gradient n. This lead speed nv is
 ascertained individually for each controlling element. Lead speed nv
 corresponds to an instantaneous speed which is before the actual setpoint
 speed at which a setpoint value of the charge should be reached. Speed
 pattern n, shown in FIG. 3, clarifies the relative position of lead speed
 nv and of setpoint speed ns. One can see that setpoint speed ns is reached
 at instant ts. Lead speed nv is already reached at instant tv which is
 before instant ts. The diagram shows clearly that the interval between the
 two instants ts and tv is a function of the speed gradient. That is to
 say, the greater the speed gradient n, the further lead speed nv is before
 setpoint speed ns, in order to achieve the time interval between ts and tv
 predefined by the reaction time of the respective controlling element.
 Ideally, for each controlling element there is a family of characteristics
 which is a function of setpoint speed ns and speed gradient n, and from
 which lead speed nv can be gathered. Charge characteristic F shown in FIG.
 3 clarifies again that, if a controlling element is triggered at instant
 tv, the charge reaches its setpoint value Fs punctually at instant ts.
 In the fourth method step 23, it is queried whether instantaneous speed n
 has reached lead speed nv. If this is so, in the next method step 24, the
 respective controlling element to which lead speed nv is allocated is
 triggered. The charge change resulting after the triggering of individual
 or all the controlling elements is converted by appropriate adjustment of
 the injection time and/or of the ignition-advance angle. As shown by block
 26 in FIG. 2, this procedure is carried out directly after method step 24.
 In the last method step 25, it is queried whether instantaneous speed n has
 reached setpoint speed ns. Namely, if this is the case, charge setpoint
 value Fs is reached, and specifically on condition that each controlling
 element has been triggered at lead speed nv ascertained for it
 individually. The triggering process for the controlling elements can then
 be started anew, beginning with the detection of the driver's input.