The invention relates to a method for controlling an internal combustion engine fitted in a motor vehicle and comprising automatic gearing.

In electronically controlled automatic gearing, a so-called starter clutch is closed upon starting. This clutch is controlled solely hydraulically and cannot therefore be influenced electronically. The timing of the closing behaviour is essentially dependent upon the temperature of the gearing and the hydraulic oil.

In the event of high engine moments occuring at the moment of engaging the driving stage from the position N into the position D or from the position N into the position R as a result of acceleration prior to the engagement of the driving stage, then the starter clutch is subjected to a high degree of wear, particularly in the case of cold gearing, which results in long clutch closing times.

It is the object of the invention to reduce the wear of the clutch.

This object is attained by way of the main claim.

According to the invention, immediately before the driving stage is engaged, a test is carried out in order to ascertain whether the engine moment exceeds a given threshold value, in which case the engine moment is reduced by interrupting the fuel supply.

The recognition of a high engine moment is effected by processing one or more of the following data:

testing the load by means of an air mass measuring device testing the rotational speed testing a selector lever sensor, which indicates whether or not a driving stage is engaged.

In addition, the moment reduction is rendered dependent upon the driving velocity, the load and rotational speed at the moment of engagement of the driving stage, and the engine temperature.

If the load or rotational speed lie above a threshold value, whilst the vehicle velocity lies below a threshold value, then the engine moment is reduced for the engagement of the driving stage by momentarily interrupting the fuel injection. This interruption occurs for a defined period of time, namely so long as the rotational speed threshold is exceeded. The defined period of time is selected as a function of the temperature and corresponds approximately to the period of time until the closure of the clutch. In this respect, the rotational speed fluctuates around the engine temperature-dependent rotational speed threshold during this defined period of time.

Alternatively or in addition to the above, a test can be carried out to determine whether the starter clutch is closed. To this end, a further rotational speed threshold is tested. In this manner, it is ensured that the moment restriction is lifted as soon as the closed clutch is detected, so that the acceleration capacity of the vehicle does not suffer from the performance or moment reduction during the coupling procedure.

In order to recognise the closed clutch, the fuel interruption is immediately deactivated if the rotational speed falls below a further threshold, even if the above-mentioned defined period of time has not yet lapsed.

In this respect, it is expedient to activate the above-mentioned functions leading to a recognition of the closed clutch so long as the engine temperature falls within a first range, and to deactivate said functions as soon as the engine temperature falls within a further range.

The invention is explained in the following with reference to the drawings, in which:

Fig. 1 is a schematic circuit diagram for carrying out the invention, and

Fig. 2 shows an operating sequence.

In Fig. 1 , the reference number 10 designates a block representing the internal combustion engine of the motor vehicle. This internal combustion engine 10 is connected with an automatic gearing 12 via corresponding components 14. A clutch is associated with the automatic gearing 12.

For controlling the engine gearing unit a switching device 16 is provided for the automatic gearing as well as a conventional engine management system 18. Via inputs 20, 22, 24 and 26, the engine management system 18 receives data, relating amongst other things to the rotational speed, the velocity of the motor vehicle, the temperature of the engine and other characteristic operating values. A data exchange takes place between the engine management system 18 and the automatic gearing switching device 16 via data lines 28 and 30.

In addition, the engine management system 18 controls the internal combustion engine 10, for example via a line 32, which relays the ignition pulses, and via the actuation of the injection valves. The injection valves are schematically indicated by the reference number 36 and are actuated by the engine management system 18 via control lines 34.

The operating sequence according to the invention of this schematic circuit diagram is illustrated in Fig. 2:

A first stage monitors whether the driving stage switch is engaged from the parking position into the reversing position or from the neutral position into a driving stage. This driving stage switch is usually the selector lever of the automatic gearing.

A second stage monitors whether the vehicle is set in motion, i.e. whether the velocity of the vehicle lies above a threshold value. In addition, it is necessary for the rotational speed and/or the load to exceed a minimum value in order to activate the engine moment reduction according to the invention.

One of two branches can then be activated. The actuation, schematically illustrated by the switches 1 and 2, can be dependent upon the engine temperature. If the engine temperature lies below a threshold value, then the first branch is activated, whereas if the engine temperature lies above a threshold value the second branch is activated. One of the two switches 1 or 2 is opened, the other switch closed in each case.

In both branches a timing stage is provided, which ensures that the fuel interruption for moment reduction only occurs for a period of time not exceeding a threshold value to. So long as the time does not exceed this threshold value, then the rotational speed is tested, which must lie above a first threshold value no in order for the fuel interruption to be activated.

The branches 1 and 2 differ in that a second rotational speed test takes place in the branch 2 to determine whether the starter clutch is closed. So long as the rotational speed does not exceed this second threshold value, the clutch is not yet closed. If the second rotational speed threshold is exceeded, then the fuel interruption is deactivated in all cases.

If the above conditions are fulfilled, measures are adopted for reducing the engine moment. To this end, the fuel injection can be reduced via the fuel injection valves, as illustrated by way of example in Fig. 1.