EP1425503B1 - Method and device for controlling an internal combustion engine on a vehicle - Google Patents

Description

The invention relates to a method and a device for controlling an internal combustion engine of a vehicle.

In connection with the control of internal combustion engines, e.g. To protect the internal combustion engine or components or to limit the mileage of the vehicle, etc., at least one operating variable is limited to a predetermined maximum value. Examples of this are speed limits, torque limits or driving speed limits. As a rule, the aim is to comply with the limit value as precisely as possible and to comfortably adjust the operating variable to the limit value without overshoots. An example of this is known for a maximum speed limitation of an internal combustion engine from DE 195 06 082 A1, where, starting with a starting value below the limit value, the throttle valve angle is suddenly reduced in order to avoid overspeeding of the speed beyond the limit value.

Another implementation of a speed limitation is described in DE 33 19 025 A1. There is when the The limit value of the ignition angle is adjusted and / or the air / fuel mixture becomes leaner by adjusting the injection time accordingly in order to limit the engine speed to the limit value.

The document EP 1 079 029 discloses a further method for speed limitation. In this method, a switch is made from influencing the air supply to an ignition angle intervention if the deviation between the current speed and a reference value exceeds a certain threshold value.

In some applications, realizing the limitation by influencing the air supply, for example via a throttle valve, leads to a tendency to oscillate due to the dead time of the controlled system and / or due to the sudden removal of the torque, in particular when the operating variable settles to the limit value. When using the ignition angle adjustment as a limiting manipulated variable, the exhaust gas becomes very hot because of the late-drawn ignition angle and may therefore damage the catalytic converter and / or other components in the area of the exhaust gas tract. There is therefore a need to optimize a limiting function.

Advantages of the invention

The conflict of objectives described is avoided by first, e.g. when the limit value or a value derived therefrom is reached, an intervention in the air supply is carried out during which no ignition angle intervention is permitted. If the operating variable to be limited approaches the limit value, the ignition angle intervention is permitted for the rapid and vibration-free adjustment of the operating variable to be limited to the limit value. It is thereby achieved that the exhaust gas no longer becomes so hot due to the reduced operating range of the ignition angle range, and on the other hand there is sufficient dynamics.

The risk of damage to the catalyst and / or other components is reduced in a particularly advantageous manner.

It is also advantageous that the subsequent ignition angle intervention enables a gentle adjustment to the limit value, so that driving comfort is not impaired by the procedure described. It is particularly advantageous that the tendency to vibrate is greatly reduced due to the dead time of the route or if the moment is suddenly removed.

Further advantages result from the following description of exemplary embodiments or from the dependent patent claims.

drawing

The invention is explained below with reference to the embodiments shown in the drawing. Figure 1 shows an overview of a control device for controlling an internal combustion engine. FIG. 2 shows a preferred procedure for limiting a selected operating variable of the internal combustion engine, using the example of the speed, on the basis of a flow chart. Finally, the mode of operation of the limitation is illustrated in FIG. 3 on the basis of time diagrams.

Description of exemplary embodiments

Figure 1 shows an overview of a control device 10, which consists of input circuit 12, microcomputer 14 and output circuit 16. These components are connected to one another with a bus system 18. The control device 10 represents an electronic engine control unit for controlling the internal combustion engine, the functions for the engine control known to the person skilled in the art from the prior art being used. With regard to the procedure described below for limiting a company size A signal is fed to the internal combustion engine or the vehicle of the control unit 10, there the input circuit 12 via an input line 20 from a measuring device 22, which represents the operating variable to be limited, in the exemplary embodiment described below the engine speed nmot.

Further operating variables of the internal combustion engine and / or the vehicle are fed from measuring devices 30 to 34 to the control unit 10 via further input lines 24 to 28, which are not specified in any more detail. These operating variables are the variables necessary for the functions performed by the control unit 10 to control the internal combustion engine, e.g. Accelerator pedal position, engine temperature, exhaust gas composition, supplied air mass, intake manifold pressure, etc.

The control units 10 output the manipulated variables for setting performance parameters of the internal combustion engine via the output circuit 16. In the exemplary embodiment of an internal combustion engine, these are primarily the air supply, ignition angle setting and fuel metering. This is symbolized in FIG. 1 by the output lines 36 for controlling the air supply, 38 for controlling the fuel metering and 40 for controlling the ignition angle.

The procedure described below for limiting an operating variable of the internal combustion engine and / or the vehicle is implemented in the microcomputer 14 as a program, which determines output variables for controlling the internal combustion engine in terms of limiting the operating variable depending on the input variables. Such a program for limiting the operating variable represents an independent object of the invention. The procedure for limiting using a speed limitation is described below. However, the procedure shown is in other exemplary embodiments with other operating variables, for example in connection with a driving speed limit, a torque limit, etc. The advantages mentioned at the outset are achieved in the same way as for speed limitation.

In addition to the limiting function, the control unit also carries out the other motor control functions, likewise with the aid of programs from the microcomputer. For example, the torque of the internal combustion engine is adjusted by adjusting the manipulated variables depending on the accelerator pedal position and other operating variables.

To limit the speed, the engine speed or a variable derived from the engine speed (for example a so-called predicted speed) is compared with a maximum speed. The predicted speed is derived from the measured engine speed and its gradient, such that if the predicted speed exceeds the maximum speed, it can be assumed that the actual speed will exceed the maximum speed in the near future. If the actual size to be limited exceeds a maximum value, an intervention in the air supply is made via an amplifier of the limiter, in particular the throttle valve is closed. No ignition angle intervention is permitted during this process. If the size to be limited (engine speed or predicted speed) reaches or exceeds the maximum speed, in one advantageous exemplary embodiment, injections to individual cylinders are hidden. If the variable forming the control signal for influencing the air supply has become smaller than a predetermined threshold value and / or the difference between the limit value and the actual speed in a predetermined band, the ignition angle intervention is released and the speed settling to the limit value by means of Ignition angle adjustment, thus implemented with high accuracy and dynamics. In one embodiment, there is no need to hide injections.

Depending on the exemplary embodiment, the maximum speed limit value is compared with the predicted speed value or a speed limit value derived from the maximum speed limit value is compared with the actual engine speed to trigger the limiting process described above. In both cases, the choice of procedure effectively avoids the heating of the exhaust gas and / or vibrations during settling.

As mentioned above, in the preferred exemplary embodiment the limiting function is implemented as a program of the microcomputer 14. This program is outlined in FIG. 2 using a flow chart. The individual elements of the flow diagram shown in FIG. 2 represent program parts or program steps, while the connecting lines outline the information flow.

The illustration according to FIG. 2 shows a preferred exemplary embodiment for limiting the engine speed. In other exemplary embodiments, the limitation is used in an analogous manner to limit the torque, the vehicle speed, etc.

First of all, a predetermined speed limit value Nlimit or one that can be influenced by the driver is predetermined in 100. This is fed to a link point 102, in which this limit value is compared with a predicted speed value Npräd. The predicted speed is determined in 104 depending on the engine speed Nmot. One exemplary embodiment consists in increasing the engine speed by a factor which is derived from the gradient of the engine speed is. The deviation Δ between the limit speed and the predicted speed determined in 102 is fed to an integrator 106, a comparator 108 and an amplifier 110. An integration constant I is fed from the memory 112 to the integrator 100. The integration constant is either fixed or depends on the size of the company. It is dependent, for example, on the speed or speed deviation, a larger constant being provided as the speed deviation becomes smaller or the speed increases. Correspondingly, the proportionality factor P is determined in 114 and fed to the amplifier 110. Here, too, the factor is either predefined or dependent on the operating variable, for example depending on the speed or dependent on the speed deviation.

Depending on the speed deviation Δ and the integration constant, the integrator forms an output signal which is led to the junction 116. Correspondingly, the amplifier 110 forms an output signal from the speed deviation Δ and the proportionality constant P, which is fed to the junction 116. Both output signals are linked, in particular added, and output as an output signal for the torque control. Thus, when the limit speed N limit is exceeded by the predicted speed, that is to say in the case of a negative deviation value Δ, a jump back in the torque is carried out due to the proportionality gain in 110 in order to regulate the predicted speed to the limit speed. The output signal formed according to FIG. 2 is passed on, preferably as part of a minimum value selection, instead of the driver's setpoint or other setpoints for setting the torque. In this phase of the speed limitation, the ignition angle intervention is prohibited. The torque specified by the output signal is implemented So only via the control of the air supply, possibly the force metering, not by adjusting the ignition angle.

In order to release the ignition angle intervention via the signal zwfre, the speed deviation is compared in comparator 106 with limit values a and / or b. If the speed deviation is in a band between predetermined values a and b or in other versions below the upper or above the lower limit value, a corresponding signal is supplied to the AND link 118. Furthermore, the output signal of the proportionality amplifier 110 is compared in a comparator 120 with a threshold value S. If the output signal falls below this threshold, i. H. if it is less than the threshold value or, in the case of negative values, greater than this, a corresponding signal is sent to the AND link. In this case, the signal zwrei is formed and the ignition angle intervention is released when the speed deviation is within the intended range and the output signal of the proportionality amplifier is less than the predetermined threshold value. In other applications, only one of the mentioned criteria for releasing the ignition angle intervention is checked. The other criterion can then be missing.

The solution described above works on the basis of a comparison of the predicted speed with a limit speed. In other exemplary embodiments, the actually measured engine speed is used instead of the predicted speed, the limit speed not the actual limit speed, but a derived one, e.g. variable variable depending on the speed and speed gradient, e.g. in the prior art mentioned at the beginning.

In this context, firing angle release means that the setpoint torque value which corresponds to the combined output signal of the amplifier 110 and the integrator 100 corresponds, not only by influencing the air supply, possibly the fuel metering, but also by influencing the ignition angle.

The procedure illustrated is illustrated in greater detail on the basis of the time diagrams in FIG. 3. Figure 3a shows the time course of the engine speed Nmot and the predicted speed Npräd, Figure 3b shows the course of the throttle valve position a and Figure 3c shows the time course of the ignition angle ZW.

FIG. 3a shows a situation of the engine speed increasing in the direction of the limit value N limit. The predicted speed Npräd is shown in dashed lines, and the actual engine speed Nmot is drawn through. The predicted speed is derived from the motor speed, taking its gradient into account. At time t1, the predicted speed Npräd exceeds the limit value N Limit, ie the controller sees a negative deviation between the limit speed and the predicted speed. According to FIG. 3b, this leads to a sudden reduction in the throttle valve position α from time t1. Accordingly, the speed increase is slowed down, which leads to a greater slowdown in the increase in the predicted speed due to the decreasing gradient. At time t1, the ignition angle is not adjusted, as shown in FIG. 3c. At time t2, the deviation between the predicted speed Npräd and limit speed N Limit occurs in the intended range. Furthermore, at time t2 according to FIG. 3b, the proportional component of the limiting controller is smaller than the intended limit value, so that from time t2, the ignition angle is released and the relatively small residual speed deviation is corrected by retarding the ignition angle as shown in FIG. 3c.

As described above, the procedure described is carried out not only in connection with a speed limitation, but also in connection with other operating variables for its limitation, for example for limiting the torque, for limiting the driving speed of a vehicle, etc.

Claims (8)

1. Method for controlling an internal combustion engine of a vehicle, an operating variable (Nmot) of the internal combustion engine or of the vehicle being sensed, this operating variable (Nmot) being limited to a predefined limiting value (Ngrenz), the limitation being carried out by influencing the air supply to the internal combustion engine, characterized in that at first the air supply (36) is influenced in order to limit the operating variable (Nmot) to the limiting value (Ngrenz), and an ignition angle intervention (40) is then performed, in that the ignition angle intervention (40) is enabled if the difference between the limiting value (Ngrenz) and operating variable (Nmot) is limited in absolute terms in the upward direction (a, b) and/or a second control variable for influencing the torque of the internal combustion engine, which is formed as a function of the difference between the limiting value (Ngrenz) and operating variable (Nmot) by means of a proportional amplifier (110), drops below a predefined threshold value (S) in absolute terms.
2. Method according to Claim 1, characterized in that a predicted operating variable (Npräd) is formed as a function of the operating variable (Nmot) and its gradient, and is compared with the limiting value (Ngrenz).
3. Method according to one of the preceding claims, characterized in that the operating variable is the engine speed, the predicted speed, an engine torque or the velocity of the vehicle.
4. Method according to one of the preceding claims, characterized in that a first control variable is formed as a function of the difference between the limiting value (Ngrenz) and operating variable (Nmot, Npred) by means of an integrator (106), the second control variable is formed by means of the proportional amplifier (110), and both variables form a resulting control variable for influencing the torque of the internal combustion engine.
5. Method according to one of, the preceding claims, characterized in that the limiter determines a setpoint value for a torque of the internal combustion engine, and from this setpoint value and further setpoint variables for the torque a resulting setpoint value for controlling the internal combustion engine is formed, which setpoint value is implemented by influencing the air supply (36), if appropriate the fuel metering means (38) and, if permitted, by ignition angle adjustment means (40).
6. Device for controlling an internal combustion engine of a vehicle, having a control unit (10) which senses a value for an operating variable (Nmot), compares this operating variable (Nmot) with a predefined limiting value (Ngrenz) and, as a function of the comparison, controls the internal combustion engine in order to limit the operating variable (Nmot) to the limiting value (Ngrenz), characterized in that at first only the air supply (36) of the internal combustion engine is influenced, and then an ignition angle intervention (40) is enabled, the ignition angle intervention (40) being enabled if the difference between the limiting value (Ngrenz) and operating variable (Nmot) is limited in absolute terms in the upward direction (a, b) and/or a second control variable for influencing the torque of the internal combustion engine, which is formed as a function of the difference between the limiting value (Ngrenz) and operating variable (Nmot) by means of a proportional amplifier (110), drops below a predefined threshold value (S) in absolute terms.
7. Computer program having program coding means in order to carry out all the steps of any of Claims 1 to 5 if the program is run on a control device.
8. Computer program product with program coding means which are stored on a computer-readable data carrier in order to carry out the method according to any of Claims 1 to 5 if the program product is run on a control device.