EP0283562B1 - Idle speed control system for a combustion engine - Google Patents

Description

The invention relates to a system for controlling the idle speed of an internal combustion engine, an actuating variable being supplied to an actuator, which is determined by comparing the actual speed value, which is supplied as a speed signal, with a speed setpoint.

In the known systems for controlling the idle speed of an internal combustion engine, the actuator, which is arranged in a so-called bypass on the throttle valve, is opened wide when the internal combustion engine is cold, so that a sufficiently high idle speed is achieved. With the same opening of the actuator, however, when the engine is warm, the speed is outside the idle speed range permitted for safety reasons. If the speed signal fails - for example due to an open circuit or short-circuit of the encoder - a speed that is too low is simulated, whereupon the controller opens the actuator wide, which results in an idling speed that is too high when the engine is warm.

For example, in a device for regulating the idling speed according to GB-A-2 142 171, in the event of irregularities in a signal from a speed sensor, the regulation is switched off and a by-pass valve is controlled to its largest opening. This may result in excessive idle speed and dangerous driving conditions.

The object of the present invention is to avoid such effects as a result of the absence of the speed signal.

The system according to the invention is characterized in that if the speed signal fails, the actuator is supplied with a predetermined manipulated variable which causes a position of the actuator which differs from the end position in the direction of maximum speed
is dependent on the temperature of the internal combustion engine. As a result, the idling speed can be kept constant within reasonable limits even if the speed signal fails, so that emergency operation is possible.

An advantageous embodiment of the invention is that the speed signal is formed by speed pulses, the repetition frequency is proportional to the speed of the internal combustion engine, that a counter, the counting pulses of higher frequency are reset by each of the speed pulses and that the actuator when the counter overflows the specified manipulated variable is supplied.

In the event of a transition from idle mode to driving mode, the actuator would be closed as far as possible without any further measures due to the associated increase in the actual speed value. As a result, when the accelerator pedal reaches the idle position again, the internal combustion engine can only reach the intended idle speed again after a delay - possibly even stop. In known idle speed controllers, the operating point of the controller is therefore stored during the transition from idle mode to driving mode. For this purpose, among other things, a so-called idle contact is provided on the accelerator pedal, with which an idle signal is emitted when the accelerator pedal is in the idle position.

However, if the idle signal fails to appear, this can result in an excessive engine speed that is outside the idle range and can therefore also lead to dangerous driving situations. This is caused by the regulator opening required to start the engine. However, the controller cannot perform a necessary shutdown if - as mentioned above - the idle signal is missing. It is therefore the task of another development to enable emergency running in the absence of an idle signal.

This development is characterized in that a signal (idle signal) is also supplied, which depends on whether the accelerator pedal is in the idle position, that in the absence of the idle signal, the actual speed value is not used to determine the manipulated variable, and that the actuator has one predefined manipulated variable is supplied when the idle signal is not available and the speed setpoint is greater than the actual speed value for a predetermined time.

An advantageous embodiment of this development consists in that the predetermined actuating variable is only supplied to the actuator if, after the predetermined time has elapsed, the actual speed value is not less than the predetermined speed value when the internal combustion engine was started.

Another development of the invention reduces the effects of the absence of a supplied signal, which represents the engine temperature, by assuming a predetermined temperature if the supplied signal is outside a predetermined range.

Advantageous further developments and improvements of the invention specified in the main claim are possible through the measures listed in the further subclaims.

The invention allows numerous embodiments. Two of these are shown schematically in the drawing using several figures and described below. It shows:
1 parts of the system according to the invention insofar as they are necessary to explain the invention,
2 the manipulated variable as a function of the engine temperature,
3 shows a section of a program of the microcomputer,
Fig. 4 shows a section of another program of the microcomputer and
Fig. 5 shows another program section.

The system shown in FIG. 1 comprises a controller which essentially consists of an integrated circuit which contains a microcomputer 1 and an analog / digital converter 2. A speed signal is fed to the controller from a speed sensor 3 - for example, a predetermined number of pulses per revolution of the internal combustion engine. An actuator 4, which adjusts the cross section of a so-called bypass 5, is controlled by comparison with a stored target value. The bypass 5 represents the bypass of a schematically indicated throttle valve.

Since the required amount of air depends on the engine temperature, the adjustment range of the actuator 4 is narrowed according to the engine temperature, which is shown schematically in FIG. 2. An upper and a lower modulation limit A _o and A _{u are provided} for the actuator 4, which decrease with increasing temperature. Corresponding values are stored in a memory assigned to the microcomputer for each subrange of the temperature.

If the microcomputer 1 receives no speed pulses, the actuator 4 is supplied with a predetermined manipulated variable which, according to a development of the invention, is dependent on the engine temperature. The corresponding curve is designated S in FIG. 2. An easy way to check for existence of speed pulses is explained using a flow chart which is shown in FIG. 3. In a manner known per se, a speed measurement is performed within a part of the program (not shown) by counting pulses of a higher frequency between two successive speed pulses. This counter is reset with every speed pulse after its counter status has been transferred to a register. If the speed pulses do not occur, an overflow results when the counter is appropriately dimensioned, whereupon a flag is set. In the program part shown, a query is made at 31 as to whether the flag is set or not. If the flag is set, the specified value for the manipulated variable is called at 32. If the flag is not set, then speed control takes place at 33 in a manner known per se by comparing the target and actual speed values.

In order to be able to take into account in the idle speed control whether the accelerator pedal is in the idle position, an idle switch 16 (FIG. 1) is provided, the signal of which, in the following idle signal, is processed in the microcomputer 1 as follows using the program shown in FIG. 4 becomes.

If it is determined at 41 that an idle signal is present, the idle speed control is carried out as usual at 42. However, if there is no idle signal, it is checked whether the speed setpoint is greater than the speed actual value. If this is the case, the parts 42 of the program which effect speed control are bypassed. This ensures that the accelerating by accelerating speed values no longer influence the manipulated variable supplied to the actuator. However, it is still possible to influence the temperature.

If the driver takes his foot off the accelerator pedal, the idle switch 16 (FIG. 1) is closed again, so that the idle signal is present again and the speed-regulating program part 42 is addressed again.

However, if there is a defect so that no idle signal occurs despite the accelerator pedal returning to the idle position, there is no idle speed control. This can lead to a dangerous driving situation, for example, if bypass control 5 (Fig. 1) was opened very wide by the last speed control performed, remained in this position during the intermittent accelerating and is not reduced again after the accelerating due to the missing idle signal.

In the case of the malfunction described, the speed setpoint is less than the actual value, but this can also occur briefly in normal operation. The program steps described below are therefore used to check whether, in the event of no idle signal and a speed setpoint that is less than the actual speed value, the question is asked at 44 whether a flag is set. If this is not the case, a time specification is started at 45 and the flag is then set at 46. A decision is then made at 47 as to whether the time limit has expired. If not, it means that the query at 48 is bypassed. If, however, the time specification no longer runs, a check is made at 48 to determine whether the start value is greater than the control value. The start value A _o (FIG. 2) and the control value correspond to any value between A _u and A _o . If applicable, the program is continued normally, while otherwise a predetermined manipulated variable is called up at 49 and fed to the actuator.

A further development of the invention is explained below with reference to FIGS. 1 and 5, with which a malfunction due to a defect in the area of a temperature sensor and its supply line is prevented.

In the embodiment shown in FIG. 1, the regulator 1 is fed by an operating voltage (+), which is obtained from the battery voltage + U _B with the aid of a resistor 6 and a Zener diode 7. The motor temperature is now measured in such a way that the stabilized voltage is fed to an NTC resistor 9 via a second resistor 8. The NTC resistor 9 is located at a suitable point on the motor, while the controller, including the few discrete components shown in FIG. 1, are located in a corresponding housing. A connection between the NTC resistor 9 and the regulator circuit is established by a line 10 which is provided with plug devices 11, 12 at both ends.

The circuit point 13 represents the input for the temperature signal and is connected via a resistor 14 to the input of the analog / digital converter 2. The level of the voltage supplied to the analog / digital converter accordingly depends on the value of the NTC resistor 9 and thus on the Engine temperature.

In the event of a short circuit in the area of the NTC resistor 9 or a short to ground of the signal line 10, the voltage at the input 13 assumes ground potential, which is determined in the microcomputer, whereupon the modulation limits A _on and A _un shown in dashed lines in FIG. 2 are specified. If the signal line 10 is interrupted, the voltage at the input 13 becomes equal to the positive operating voltage (+) of the microcomputer, which also leads to the application of the specified modulation limits. The same applies to an end of the signal line with a line which carries a higher voltage, for example the operating voltage + U _B. In this case, a resistor 14 and a diode 15 are provided. The latter then becomes conductive and thus prevents the input voltage of the analog / digital converter from rising significantly above the operating voltage of the microcomputer or the analog / digital converter.

5 shows parts of a program as a flow chart, which are used to check the input signal U _{NTC of} the analog / digital converter 2 and to convert to so-called emergency operation. First, it is determined at 21 whether U is _NTC ≧ U _Z. If this is the case, at 23 the modulation limits A _o and A _{u are set} equal to the values A _on and A _un specified for emergency operation. If U _{NTC is} smaller than U _Z , it is checked at 22 whether U _NTC = 0 (mass). If applicable, the program also continues at 23. However, if U _NTC > 0, the modulation limits A _o and A _{u are} determined at 24 as a function of the temperature.

Claims (8)

1. System for controlling the idling speed of an internal combustion engine, an actuating element being supplied with an actuating variable which is determined by means of a comparison of the engine speed actual value, which is supplied as an engine speed signal, with an engine speed reference value, characterised in that, in the event of the failure of the engine speed signal, the actuating element is supplied with a predetermined actuating variable, which is dependent on the temperature of the internal combustion engine and which brings about a position of the actuating element which differs from the final position in the direction of maximum engine speed.
2. System according to Claim 1, characterised in that the engine speed signal is formed from engine speed pulses, the repetition rate of which is proportional to the engine speed of the internal combustion engine, in that a counter which is supplied with counting pulses of a relatively high freguency is reset by each of the engine speed pulses, and in that, in the event of the counter overflowing, the predetermined actuating variable is supplied to the actuating element.
3. System according to one of the preceding claims, characterised in that, in addition, a signal (idling signal) is supplied which is dependent on whether the accelerator pedal is in the idling position, in that in the absence of the idling signal the engine speed actual value is not used to determine the actuating variable, and in that the actuating element is supplied with a predetermined actuating variable if the idling signal is not present and the engine speed reference value is smaller than the engine speed actual value for longer than a predetermined time.
4. System according to Claim 3, characterised in that the actuating element is only supplied with the predetermined actuating variable if, after the predetermined time has expired, the engine speed actual value is greater than the engine speed reference value predetermined at the start of the internal combustion engine and the start value is not greater than the control value.
5. System according to one of the preceding claims, characterised in that, in addition, a supplied signal is evaluated which reproduces the engine temperature, and in that a predetermined temperature is assumed if the supplied signal lies outside a predetermined range.
6. System according to Claim 5, characterised in that the actuating element is supplied with an actuating variable, the value of which lies between a lower and upper control limit, in that the control limits are dependent on the supplied signal, and in that predetermined control limits become active if the supplied signal lies outside the predetermined range.
7. System according to one of Claims 5 or 6, characterised in that a microcomputer (1) having an analog-to-digital converter (2) is constructed as controller, in that a temperature-dependent resistor (9) is connected via a line (10) in series with a resistor (8) arranged in the region of the microcomputer (1), in that the series connection is fed with a stabilised voltage which is also fed to the microcomputer (1), and in that the terminal of the resistor (8) facing the line (10) is connected to the input of the analog-to-digital converter (2).
8. System according to Claim 7, characterised in that a further resistor (14) is provided between the line (10) and the input of the analog-to-digital converter (2), and in that the input of the analog-to-digital converter (2) is connected to the input of the microcomputer for the stabilised voltage via a diode (15).

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