Abstract:
A method is described for detecting the independent running and/or the start/stop of an internal combustion engine, in which parameters of the internal combustion engine characterizing the combustion process, especially pressure changes or vibrations, are evaluated for this detection.

Description:
RELATED APPLICATION INFORMATION 
     The present application claims priority to and the benefit of German patent application no. 10 2010 039 800.4, which was filed in Germany on Aug. 26, 2010, the disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a method for detecting the independent running of an internal combustion engine which is tow-started from its position of rest by a start-assist apparatus, as well as a device for implementing the method. 
     BACKGROUND INFORMATION 
     Internal combustion engines of a motor vehicle are not able to initiate their active operation independently. For this reason, in conventional vehicles, the internal combustion engines are set in motion by an electrically operated starter. The necessary processes of mixture formation, combustion, engine-speed sensing and charge sensing of the internal combustion engine are started simultaneously with the operation of the starter. The independent running of the internal combustion engine is recognized when the speed of the internal combustion engine is above the speed of the starter or when the speed of the internal combustion engine exceeds a defined threshold. When the internal combustion engine has started to move independently, the starter is decoupled again from the internal combustion engine. 
     In hybrid systems which have two power plants in the form of the internal combustion engine and an electric motor, the internal combustion engine may be started by the electric motor or by the starter. With such a hybrid drive, it is possible to start the internal combustion engine from the motor-vehicle standstill. However, it is also possible to start the internal combustion engine during operation solely on electrical power with the electric motor as drive. The transition from electrical operation to hybrid operation, in which the electric motor or the starter starts the internal combustion engine and the vehicle is then powered by the electric motor and the internal combustion engine, may be initiated in the following manner. An interrupting clutch, situated between the internal combustion engine and the electric motor, is closed, and the electric motor tow-starts the internal combustion engine until the internal combustion engine is running on its own. 
     A further possibility is that the interrupting clutch between the internal combustion engine and the electric motor is initially open. While the vehicle is in operation, the interrupting clutch is then closed in a dragging fashion in the form of a proportional clutch or abruptly with the aid of an impulse clutch or a proportional clutch. In the cases described, it is not possible to say whether the internal combustion engine is running independently based on the analysis of the speed of the internal combustion engine, since the internal combustion engine may be pulled along by the electric motor. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the exemplary embodiments and/or exemplary methods of the present invention is to reliably detect an independent running of the internal combustion engine for the load case of the internal combustion engine (e.g., transition from electrical motoring to hybrid motoring or hybrid motoring with recuperation requirement). 
     The objective is achieved according to the exemplary embodiments and/or exemplary methods of the present invention by evaluating parameters characterizing the combustion process, especially pressure changes and/or vibrations, to detect the independent running of the internal combustion engine. This has the advantage that a signal is utilized which is produced solely by the working mode of the internal combustion engine. In this context, influence by the electric motor is not possible, since a signal is considered which draws upon the combustion processes, that are caused in the internal combustion engine by its active running, for assessing an independently running internal combustion engine. 
     In one variant, the signal of a knock sensor, disposed on the internal combustion engine, is evaluated. The use of a knock sensor for recognizing the independent running of the internal combustion engine, which detects structure-borne-noise vibrations on the housing of the internal combustion engine caused by the combustion process, falls back upon sensors normally mounted on the internal combustion engine. Suitable evaluation electronics for the signal from the knock sensor are also already available in the motor vehicle, so that it is possible to dispense with additional components in terms of hardware in order to carry out the method. Merely one software change allows the signal of the knock sensor to be evaluated with respect to the independent running of the internal combustion engine. 
     Advantageously, the signal of the knock sensor is compared to a predefined reference range, and if the signal of the knock sensor falls within the predefined reference range, this is indicative of the independent running of the internal combustion engine. The selection of the reference range ensures that the signal is only able to assume values which are typical for a normal sequence of combustions within the internal combustion engine. In this context, overshoot signals of the knock sensor which take place, in particular, due to combustions that are not caused by the ignition spark of a spark plug, and which produce a very high pressure rise in the internal combustion engine, are reliably left out of consideration. 
     In one refinement, the signal of the knock sensor is evaluated in terms of its amplitude and/or in terms of its frequency. With amplitude or frequency, properties of vibrations which typically characterize the signal pattern are therefore considered. In so doing, an individual reference range is predefined for each amplitude and for each frequency for the comparison to the signal of the knock sensor, so that the amplitude is compared with an amplitude reference range and the frequency is compared with a frequency reference range. 
     In one variant, to start the internal combustion engine, an engine management outputs a signal to the start-assist apparatus and calculates at least one controlled variable for the internal combustion engine that is set at the internal combustion engine, the at least one controlled variable of the started internal combustion engine being measured, and the signal of the knock sensor being evaluated in the event the measured controlled variable has a value greater than zero. The functioning of the actuators mounted on the internal combustion engine is checked by the additional evaluation of the controlled variables, whereby it is determined whether the internal combustion engine can also really be in independent motion. 
     The controlled variables, which are set and measured by the engine management, relate in particular to the injection and/or the ignition of the internal combustion engine. Given adjusted charge, the combustion process within the internal combustion engine is controlled sufficiently with these controlled variables. Going into detail, such controlled variables may take the form of injection time, moment of ignition or crankshaft angle at which an ignition is to take place. Methods for determining such controlled variables are stored in the engine management, and therefore do not have to be additionally developed, thus saving on development time. 
     In a further refinement, the signal of the knock sensor is filtered prior to evaluation. In this manner, the signals are freed of noise, thereby permitting a precise evaluation of the knock-sensor signal. 
     Advantageously, in the event one value of the two measured controlled variables of the internal combustion engine is unequal to zero and when a value of at least one of the measured signals is outside of the corresponding reference range, a defect of one of the actuators adjusting the controlled variable in the internal combustion engine is inferred. In this case, a non-independent running of the internal combustion engine is recognized. 
     In one specific embodiment, predefined operating states of the internal combustion engine and/or of the overall system are restricted or forestalled upon recognition the internal combustion engine is not running independently. These operating states may include load-point shifts, as well as the deactivation of a start/stop functionality of the motor vehicle. 
     In one especially simple variant, a start or a stop of the internal combustion engine is recognized on the basis of the independent running of the internal combustion engine. 
     A further development of the exemplary embodiments and/or exemplary methods of the present invention relates to a device for detecting the independent running of an internal combustion engine, the device putting out a signal to a start-assist apparatus to tow-start the internal combustion engine from its position of rest. To reliably detect the independent running of the internal combustion engine after it has been started, an evaluating arrangement evaluates parameters characterizing the combustion process of the internal combustion engine, especially pressure changes or vibrations, in order to detect the independent running of the internal combustion engine. In this manner, only those signals are considered for detecting the start of the internal combustion engine which are generated solely by the internal combustion engine during the combustion process, and which are not influenced by the start-assist apparatus. 
     In particular, a signal is received from a knock sensor and evaluated when the internal combustion engine has been started. Costs are reduced by the use of sensors normally already present on the internal combustion engine. 
     The start-assist apparatus advantageously takes the form of a starter or an electric motor of a hybrid vehicle. Thus, the method of the present invention is usable both in conventional motor vehicles and in hybrid vehicles. 
     The exemplary embodiments and/or exemplary methods of the present invention permits numerous specific embodiments. One of these shall be described in detail with reference to the figures shown in the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a hybrid system. 
         FIG. 2  shows a flowchart for detecting the independent running of an internal combustion engine. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic diagram for a hybrid drive in a motor vehicle. An internal combustion engine  1  is connected to an electric motor  3  via a drive shaft  2 . Electric motor  3  is seated on drive shaft  2  of the drive train of the motor vehicle. Situated between internal combustion engine  1  and electric motor  3  is an interrupting clutch  4 , which in the open state, allows the motor vehicle to operate solely on electrical power using only electric motor  3 . Electric motor  3  is connected to a transmission  5  that is adjacent to a differential  6 . This differential  6  is supported on a side shaft  7  that drives a vehicle wheel  8 . 
     Located between electric motor  3  and transmission  5  is a further clutch  9  that is used for starting the motor vehicle from rest and is actuated by the driver of the motor vehicle when the motor vehicle goes from the standing to the driving state. Also situated on internal combustion engine  1  is a knock sensor  10  that is connected to a control unit  11  which, in addition, is connected to electric motor  3 . 
     A hybrid vehicle is usually started up by electric motor  3  when the vehicle is at a standstill, so that initially, it is powered solely electrically. The power output to be set in respect to the hybrid vehicle is defined by the driver by actuation of an accelerator. If the power output by electric motor  3  is no longer sufficient to satisfy the driver command, control unit  11  decides that internal combustion engine  1 , up to now in the rest state, should be started. At this point, interrupting clutch  4 , which is situated between internal combustion engine  1  and electric motor  3  and is likewise connected to control unit  11 , is closed. In so doing, a rotary motion is transmitted by electric motor  3  via closed interrupting clutch  4  to drive shaft  2 , which up to now has been in a state of rest, and therefore to internal combustion engine  1 . At the same time, by demand of control unit  11 , the power output of electric motor  3  is increased, so that electric motor  3  is also able to tow-start the load of internal combustion engine  1  accordingly. In addition, at this point in time, control unit  11  calculates controlled variables for the injection such as the injection time of the injectors and the moment of ignition or the angle of the crankshaft at which the ignition should take place in the individual cylinders of internal combustion engine  1 . 
     In order to now determine whether internal combustion engine  1  is also running independently, a sequence control, shown in  FIG. 2 , starts in control unit  11 . In a signal conditioning process in block  100 , output signals  101  are received from knock sensor  10  and evaluated. These output signals  101  are conditioned in the signal-conditioning process (block  100 ) by suitable filters in such a way that output signals  101  are freed of noise and are able to be supplied in the form of evaluation signals  109  and  110  to an evaluation process. In this context, output signals  101  supplied by knock sensor  10  are differentiated into amplitude evaluation signals  109  (block  102 ) and frequency evaluation signals  110  (block  103 ). Depending upon the form of the evaluation, either amplitude evaluation signals  109  of block  102  or frequency evaluation signals  110  of block  103 , or perhaps also both types of signals may be considered for assessing the independent running of internal combustion engine  1 . 
     Amplitude evaluation signals  109  in block  102  or frequency evaluation signals  110  in block  103  made available are supplied to a signal evaluation process in block  104 . The signal evaluation in block  104  receives information about the injection and the ignition, respectively, measured in independently moving internal combustion engine  1 , as input signals  105 . Such input signals  105  characterize the state of internal combustion engine  1 , and are either the crankshaft angle, the moment of ignition or the injection time. 
     If these input signals  105  have a value greater than zero, the signal evaluation is carried out. During the signal evaluation, amplitude evaluation signals  109  are compared to an amplitude reference range and frequency evaluation signals  110  are compared to a frequency reference range. If amplitude values  106   a  and frequency values  106   b , supplied by knock sensor  10 , lie in the respective amplitude reference range or frequency reference range, it is assumed that internal combustion engine  1  has not only started to operate independently, but is also functioning in a correct operating state. 
     However, if it is determined in the signal evaluation in block  104  that at least one input signal  105 , which is supplied as input variable of the injection or of the ignition, is equal to zero, then in block  107 , a diagnosis is performed or there is a switchover to an error handling. If input signals  105  are unequal to zero, amplitude evaluation signals  109  and/or frequency evaluation signals  110  are taken into consideration for the diagnosis of an independently running internal combustion engine  1 . If amplitude evaluation signals  109  and/or frequency evaluation signals  110  lie outside of the corresponding reference range, in block  107 , a diagnosis is carried out or a switch is made to an error handling. As a result of the diagnosis, operating states such as the shift of the load point and/or the start/stop functionality of the motor vehicle are then no longer carried out. 
     Based on the method of the present invention, not only is it possible to reliably establish the start of the internal combustion engine, but the stop of internal combustion engine  1  may be determined, as well. In this context, the various modes with respect to the start of internal combustion engine  1  by electric motor  3  or the transition from operation solely on electrical power to hybrid operation no longer have to be taken into account explicitly. The result is that an evaluating logic may be kept simple. A precise assertion about the independent running and the stop of internal combustion engine  1  may be made on the basis of the signal from knock sensor  10 .