Method for preventing engine runaway in a vehicle comprising an automatic transmission during the transition to a mechanical transmission emergency mode, in which the transmission is shifted to neutral.

Abstract

Method for preventing engine runaway of the internal combustion engine in a vehicle comprising an automatic transmission during the transition to a mechanical transmission emergency mode, in which neutral is shifted, characterized in that, during the transition to the mechanical transmission emergency mode, a controlled speed limitation is carried out in parallel to a time-limited torque reduction in the electronic transmission control for a predefined limiting speed by means of a torque limitation as a function of the current engine speed.

Description

The invention relates to a method for preventing the engine from running through in a vehicle, comprising an automatic transmission when changing over to a mechanical transmission emergency in which a shift is made to neutral, according to the preamble of claim 1.It is known from the prior art to shift into a predefined emergency gear in transmissions of motor vehicles after activation of the mechanical transmission emergency. Since this is implemented via a main pressure circuit, the components involved in the drive train of the vehicle are significantly loaded by the inertial masses and the prevailing torque of the internal combustion engine as a function of the operating situation, which results in high wear and can lead to destruction of individual components. In order to prevent this, it is known to carry out an "emergency jump" in the context of which the shift process control, when entering the mechanical transmission emergency, issues a torque intervention request, i.e. an ignition angle intervention request with a fixed torque setpoint value, by means of which at least one load due to the torque of the internal combustion engine is significantly reduced.It is also known from the prior art to shift to "neutral" in transmissions of motor vehicles after activation of the mechanical transmission emergency, whereby overloading of the drive train is avoided. However, if the mechanical transmission emergency under load, for example at full load, is activated and the frictional connection for shifting to neutral is abruptly interrupted, the motor rotates very quickly up to the rotational speed allowed by the rotational speed limiter, disadvantageously due to the load that is omitted, which gives the driver a feeling of strangeness and impairs comfort. A execution of the "emergency jump" known from the prior art is not sufficient, due to the time limitation of an ignition angle intervention, which is only permissible for a short time, to avoid an engine runaway in such a situation and to limit the engine speed to an acceptable level.From DE 199 50 663 A1 of the applicant, a method for controlling an automatic transmission with a torque converter for a motor vehicle, in particular a stepped automatic transmission, in an emergency driving mode is known, wherein the automatic transmission has an electronic transmission control device, which continuously exchanges signals with a digital engine electronics of an internal combustion engine. In this case, it is provided that, in the emergency driving mode, a transmission-independent program module of the digital engine electronics sets a permissible maximum engine torque for the emergency driving mode as a function of an engine speed in such a way that it is limited to a minimum constant value in a range of the engine speed between zero and at least approximately a limit value at which a turbine speed of the torque converter or an equivalent variable greater than zero is detected, and is increased at an engine speed above the limit value as a function of an increase in the turbine speed.Furthermore, DE 10 2009 002 031 A1 by the applicant discloses a method for operating a drive train of a motor vehicle, wherein the drive train comprises a drive unit and a transmission connected between the drive unit and an output, wherein an engine control device for controlling and / or regulating the operation of the drive unit and a transmission control device for controlling and / or regulating the operation of the transmission is assigned to the drive unit. In the known method, it is provided that, for the execution of a shift in the transmission, the transmission control device determines on the one hand an amount of an engine torque reduction and on the other hand the type of the engine torque reduction and preset to the engine control device, wherein, on the basis of the amount of the engine torque reduction preset by the transmission control device and the type of the engine torque reduction preset by the transmission control device, the operation of the drive assembly is controlled and / or regulated by the engine control device for the purpose of reducing the engine torque provided by the same, and wherein the type of the engine torque reduction is determined by the transmission control device as a function of the amount of the engine torque reduction required for the shift to be executed, as a function of the amount of the engine torque reduction that can be realized to the maximum with the aid of an influence on the ignition angle and as a function of a comfortable execution of the shift to be executed that is requested if necessary.From DE 101 29 548 B4 of the applicant, a method for reducing the load of automatic transmissions or clutches of a motor vehicle in emergency program shifts is known, in the context of which an engine torque reduction is carried out during the emergency program shift from a normal shift program into an emergency program, wherein the following steps are carried out in the electronic transmission controller in the event of emergency operation, in which an electronic controller of the automatic transmission or clutches remains functional: diagnosing a faulty state and activating the emergency program in the electronic transmission controller; determining a setpoint value for the engine torque on the basis of operating parameters present at the time of the emergency program shift for a predefined time and forwarding these data to the electronic engine controller; triggering an engine engagement to reduce engine torque, the intensity of the engine engagement being a function of the relevant operating conditions present at the time of the emergency program shift; simultaneously hydraulically activating the shift clutches for the emergency program shift; ending the engine engagement after the predetermined time; and transitioning to the emergency driving operation.The present invention is based on the object of specifying a method for preventing engine runaway in a vehicle, comprising an automatic transmission when changing over to a mechanical transmission emergency, in which a shift to neutral is made.This object is achieved by the features of claim 1. Further embodiments and advantages according to the invention are evident from the dependent claims.Accordingly, a method for preventing the engine from running through in a vehicle, comprising an automatic transmission when changing over to a mechanical transmission emergency, in which a shift is made to neutral, is proposed, within the scope of which, when changing over to the mechanical transmission emergency, a controlled speed limitation is carried out for a predefined limiting speed as a function of the current engine speed, parallel to a time-limited torque reduction in the electronic transmission control.Due to the limited torque reduction over time, an upward speed of the internal combustion engine is prevented at the beginning of the activation of the mechanical transmission emergency running, wherein due to the controlled rotational speed limitation, which serves as an extended "emergency jump", an upward speed of the internal combustion engine is prevented in the long term. In the case of an Otto engine, the time-limited torque reduction takes place as an ignition angle intervention, which acts quickly and is limited to a short time, for example to 1.5 seconds.According to the invention, the ignition angle intervention is released by the controlled speed limitation, which is effected by way of a throttle valve adjustment in the case of an Otto engine as torque limitation. The permissible duration of the ignition angle intervention is sufficient in this case to avoid an undesired increase in the engine speed when transitioning to the controlled speed limitation by means of the throttle valve adjustment.In a diesel engine, the time-limited torque reduction takes place as a torque intervention via the injection, wherein a setpoint value is specified which prevents the internal combustion engine from rising at the beginning of the activation of the mechanical transmission emergency. The controlled speed limitation to the predefined limiting speed takes place as torque limitation via a torque intervention via the injection as a function of the current speed, wherein the setpoint value of the torque of the controlled speed limitation is determined, during both functions, namely the time-limited torque reduction and the controlled speed limitation, are active, via a minimum selection between the setpoint value of the time-limited torque reduction and the setpoint value of the torque of the controlled speed limitation.For the predefined limiting rotational speed, the profile of the maximum permissible engine torque, which serves as a setpoint value of the torque of the controlled rotational speed limiting, is preferably stored as a function of the current rotational speed in the electronic transmission control as a characteristic curve.In transmissions which have the function "controlled transmission protection" which brings about a reduction in the engine speed when engaging gear from high speed, no change in the engine control or in the signal processing is advantageously required.The invention is explained in more detail by way of example with reference to the attached figure which represents the curve of the maximum permissible engine torque at the crankshaft level as a setpoint value for the controlled rotational speed limitation for a predefined limiting rotational speed 3000 / min.According to the invention, when the transmission is transferred to the mechanical emergency transmission, in parallel with a time-limited torque reduction in the electronic transmission control, which takes place via an ignition angle intervention in the case of an Otto engine and via a torque intervention via the injection in the case of a diesel engine, a controlled speed limitation is carried out via a torque limitation as a function of the current engine speed. Here, the controlled speed limitation takes place in the case of a diesel engine as a torque limitation via a torque intervention via the injection as a function of the current speed and in the case of an Otto engine via a throttle valve adjustment as a function of the current speed.In the example shown, the engine speed in the mechanical transmission emergency is to be gently limited to approximately 3000 / min. According to the attached figure, 0 Nm crankshaft torque is output as the setpoint value at a current rotational speed of 3000 / min, as a result of which the engine, coming from lower rotational speeds, does not go beyond this rotational speed. Coming from higher speeds, the engine is held "smoothly" at this speed with a correspondingly high accelerator pedal. At a current rotational speed of 2500 / min, the setpoint value is 10 Nm, wherein the setpoint value is 50 Nm at a current rotational speed of 2000 / min and 150 Nm at a current rotational speed of 1500 / min. At a current rotational speed below 1500 / min, no torque limitation is carried out. As can be seen from the attached figure, the setpoint value is -10 Nm at a current rotational speed of 3500 / min, 3750 / min-15 Nm, 4000 / min-60 Nm and 0 Nm indicated above 4000 / min. In this way, the engine is smoothly guided to 3000 / min coming from high rotational speeds (even at 100% accelerator pedal position). The value zero for the engine torque at the crankshaft level means that the torque applied by the engine is just sufficient for supplying other consumers, such as pumps, etc. A negative value therefore means a very strong braking of the engine.The controlled speed limitation via a torque limitation may be carried out for a predefined period of time in order to prevent the engine runaway when transitioning to the mechanical transmission emergency. Alternatively, the controlled speed limitation can be carried out over the entire period during which the mechanical transmission emergency is active.

Claims

Method for preventing an engine run-through of the internal combustion engine in a vehicle, comprising an automatic transmission during the transition into a mechanical transmission emergency, in which a shift is made to neutral, characterized in that, during the transition into the mechanical transmission emergency, a controlled speed limitation is carried out for a predefined limiting speed for a predefined limiting speed in the electronic transmission control in parallel with a time-limited torque reduction, by means of a torque limitation as a function of the current engine speed.Method according to Claim 1, characterized in that, in the case of an internal combustion engine designed as an Otto engine, the time-limited torque reduction takes place as an ignition angle intervention, wherein, in the case of an internal combustion engine designed as a diesel engine, the time-limited torque reduction takes place as a torque intervention via the injection, wherein a setpoint value is predefined which prevents the internal combustion engine from rising up at the beginning of the activation of the mechanical emergency operation.Method according to Claim 1 or 2, characterized in that the controlled speed limitation is carried out as torque limitation by means of a throttle valve adjustment in an internal combustion engine designed as an Otto engine, wherein, in the case of an internal combustion engine designed as a diesel engine, the controlled speed limitation is carried out as torque limitation by means of a torque intervention via the injection, wherein the setpoint value of the torque of the controlled speed limitation is determined, while the temporarily limited torque reduction and the controlled speed limitation are active, by means of a minimum selection between the setpoint value of the temporarily limited torque reduction and the setpoint value of the torque of the controlled speed limitation.Method according to Claim 1, 2 or 3, characterized in that, for the predefined limiting rotational speed, the profile of the maximum permissible engine torque, which serves as a setpoint value of the torque of the controlled rotational speed limiting, is stored as a characteristic curve in the electronic transmission control as a function of the current rotational speed.Method according to Claim 1, 2, 3 or 4, characterized in that the controlled speed limitation is carried out for a predefined time period or over the entire time period in which the mechanical transmission emergency running is active.

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