Abstract:
An internal combustion engine has a camshaft with an adjustable phase position relative to the crankshaft. Upon starting the internal combustion engine, the phase position is derived from a crankshaft angle detected by a crankshaft sensor and a camshaft angle detected by a camshaft sensor. If the phase position is within a predetermined threshold of a predetermined phase position, a correction value is calculated based on the deviation of the phase position, otherwise, the actual phase position is equated to the phase position derived from the crankshaft angle and the camshaft angle in an emergency running mode. During normal operation the actual phase position is calculated based on the phase position, derived from the crankshaft angle and the camshaft angle, and the correction value. In the emergency running mode, at least one control signal for an actuator is determined as a function of the actual phase position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and hereby claims priority to German Application No. 10108055.7 filed on Feb. 20, 2001, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a method for controlling an internal combustion engine having a camshaft, the phase position of which is adjustable in relation to a crankshaft. 
     WO 99/43930 discloses a device for adjusting the sequence of movements of the inlet and exhaust valves of an internal combustion engine, in which the phase position of the camshaft can be adjusted in relation to a crankshaft. In this a mechanical adjusting part, which is controlled by way of a hydraulic system, is provided for adjustment of the phase position of the camshaft. The hydraulic system has a three-two-way valve, which is actuated by means of a control signal from a control device. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to create a method for controlling an internal combustion engine having a camshaft, the phase position of which is adjustable in relation to a crankshaft, the method being on the one hand reliable and on the other permitting good operability in all operating conditions of the internal combustion engine. 
     The object is achieved by the features of the independent claim. Advantageous developments of the invention are identified in the subordinate claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are explained in more detail with reference to the diagrams, of which: 
     FIG. 1 is a block diagram of an internal combustion engine, 
     FIG. 2 is a flowchart of a program for determining an actual phase position, and 
     FIG. 3 is a flowchart of a program for determining a control signal. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
     Elements having the same design and function are consistently numbered with the same reference numbers in the different figures. 
     An internal combustion engine (FIG. 1) comprises a cylinder  1  with a piston  11  and a connecting rod  12 . The connecting rod  12  is connected to the piston  11  and to a crankshaft  2 . A first gear  21  is arranged on the crankshaft  2 . The first gear  21  is mechanically coupled by way of a chain  21   a  to a second gear, which is arranged on a camshaft  3 . The camshaft  3  has cams  32 ,  33 , which act on inlet and exhaust valves  41 ,  42 . The internal combustion engine is represented with one cylinder in FIG.  1 . The internal combustion engine can obviously also have more than one cylinder. 
     An adjusting device  5  for adjusting the phase position of the camshaft  3  in relation to the crankshaft  2 , and thereby adjusting the sequence of movements of the inlet and exhaust valves, is assigned to the internal combustion engine. The adjusting device  5  has a mechanical adjusting part, which is hydraulically adjustable and thus adjusts the phase position of the camshaft  3 . The mechanical adjusting part  51  is connected by way of hydraulic lines  52 ,  53  to an actuator  54 , which preferably takes the form of a hydraulic three-two-way valve. The actuator is connected to a high-pressure hydraulic line  55  and to a low-pressure hydraulic line  56  with an oil reservoir  57 , to which an oil pump is assigned. During operation of the internal combustion engine the oil pump ensures a predetermined pressure in the oil reservoir and hence also in the high-pressure hydraulic line  55 . 
     If the internal combustion engine is in an inoperative engine condition, that is to say no combustion is taking place in the cylinder  1  and the crankshaft is not rotating, the pressure in the oil reservoir gradually subsides as therefore does the pressure in the high-pressure hydraulic line. Furthermore, the pressure in the hydraulic lines  52  and  53  also falls, as a result of which the mechanical adjusting part  51  is shifted into a limit position. 
     A control device  6  is provided, to which sensors are assigned, which register various measured variables and determine the measured value of the measured variables at any one time. As a function of the measured variables the control device  6  also determines a control signal TVAN_S not only for the actuator  54  but also for other actuators, such as a spark plug (not shown), an injection valve or a throttle valve. 
     The sensors take the form of a crankshaft sensor  71 , which registers a crankshaft angle KW of the crankshaft  2  or from the variation in the latter over time derives a rotational speed N, an air-mass flow sensor  74 , which registers the air-mass flow MAF, and a throttle valve sensor  73 , which registers a degree of opening THR of the throttle valve. Any lesser number of the sensors or also additional sensors may be provided, depending on the embodiment of the invention. 
     FIG. 1 shows a flowchart of a program, which is executed when starting the internal combustion engine and also in part, as necessary, at cyclical intervals during further operation. The program is started in a stage S 1 . This follows very soon after starting of the internal combustion engine, that is to say during the initial revolutions of the crankshaft. 
     In a stage S 2 , a sensor value PH_S for the phase position of the camshaft  3  in comparison to the crankshaft  2  is determined as a function of the registered camshaft angle NW and the crankshaft angle KW. Where necessary, this can also be done by suitable averaging or in some other way with multiple successive measured values of the crankshaft angle KW and the camshaft angle NW. 
     A predetermined phase position PH_INI from a memory is inputted in a stage S 3 . The predetermined phase position PH_INI is the phase position assumed by the camshaft  3  in relation to the crankshaft  2  when the adjusting device  51  is in its limit position, that is to say in the unadjusted position, assuming that all mechanical parts are coordinated with one another in the manner specified. On starting of the internal combustion engine, the adjusting device  51  should be in the limit position, since the hydraulic pressure will have fallen while the internal combustion engine is at a standstill. 
     In a stage S 4 , a hysteresis value is inputted, which takes account of the mechanical tolerances and fitting tolerances of the mechanical parts and also the tolerances of the crankshaft sensor  71  and of the camshaft sensor  72 . The tolerances of the crankshaft sensor  71  and of the camshaft sensor  72  typically have a determining influence on the hysteresis value HYS, while the tolerances of the other mechanical parts and the further fitting tolerances of the mechanical parts play a subordinate role here. 
     In a stage S 5 , it is analyzed whether the difference between the sensor value PH_S for the phase position and the predetermined phase position PH_INI is smaller than the hysteresis value HYS. If this is the case, the operating condition of the internal combustion engine is set to normal operation NB in a stage S 7 . 
     In a stage S 8 , a correction value PH_COR is determined as a function of the difference between the predetermined phase position PH_INI and the sensor value PH_S for the phase position. Here, this difference may be assigned directly to the correction value PH_COR, or the difference may be weighted with an evaluation factor, or averaging may be performed over successively registered values for the difference. 
     Stage S 9  is assumed for a predetermined waiting time, during which the program is preferably interrupted and other programs are run in the control device  6 . 
     In a stage S 10 , the sensor value PH_S for the phase position is determined as a function of the camshaft angle NW and the crankshaft angle KW. 
     In a stage S 11  an actual phase position PH_AKT is then calculated from the sum of the sensor value PH_S for the phase position and the correction value PH_COR. In normal operation NB the actual phase position PH_AKT is thus registered extremely precisely, assuming that errors are essentially attributable to the tolerances of the crankshaft sensor  71  and the camshaft sensor  72 . 
     Processing is then resumed at stage S 9 . Stages S 9  to S 11  are each run through cyclically in turn preferably throughout the operation of the internal combustion engine. 
     If the condition in stage S 5  is not fulfilled, that is to say the difference between the sensor value PH_S for the phase position and the predetermined phase position PH_INI is greater than the hysteresis value HYS, the processing is continued in a stage S 13 . 
     In stage S 13 , the operating condition of the internal combustion engine is set to emergency running NL. In the emergency running NL operating condition, only limited operation of the internal combustion engine is possible, with the aim of getting a vehicle provided with the internal combustion engine safely to a service workshop. In the emergency running NL operating condition there is preferably no further adjustment of the phase position of the camshaft  3  in relation to the crankshaft  2 , and the rotational speed N of the crankshaft or the driving speed of the vehicle is limited to a predetermined value. 
     In a stage S 14 , it is analyzed whether the crankshaft sensor  71  and the camshaft sensor  72  are functioning correctly. If this is not the case, the predetermined phase position PH_INI is assigned to the actual phase position PH_AKT in a stage S 15 . 
     If the condition in stage S 14  is fulfilled, however, the sensor value PH 13  S for the phase position is assigned to the actual phase position PH_AKT in a stage S 16 . The assignment in stage S 16  proceeds from the finding that in the event of this emergency running mode there is a defect present in the mechanical components determining the phase position of the camshaft  3  in relation to the crankshaft  2 . This may be a so-called chain shedding, for example, or if a belt is provided instead of the chain  21   a  a belt shedding, or an incorrectly tensioned chain or an incorrectly tensioned belt. These faults may result in variation of the phase position of up to 30 degrees or even more. 
     In a stage S 17 , the program is then stopped. Alternatively, in emergency running mode NB, the sensor value PH_S for the phase position can also be cyclically re-determined each time and stage S 16  then performed. 
     FIG. 3 shows a further program, which is performed cyclically during the operation of the internal combustion engine. The program is started in a stage S 20 . In a stage S 21  a control signal SG for an actuator of the internal combustion engine, preferably the throttle valve or the injection valve, is determined as a function of the actual phase position PH_AKT, the rotational speed N, the degree of opening THR of the throttle valve and the air-mass flow MAF. This is preferably done by means of a dynamic model of the inlet manifold of the internal combustion engine. The actual phase position PH_AKT has a determining influence on the proportion of residual gases present in the cylinder  1  prior to combustion and also on the charge itself. The fact that a precise value for the actual phase position PH_AKT is available, even in emergency running NL of the internal combustion engine, ensures good operability of the internal combustion engine in a vehicle and at the same time ensures that the emissions are low, since the air ratio in the cylinder can be precisely adjusted. In this way, good driveability as far as the nearest service workshop can still be ensured even in the case of an internal combustion engine that cannot run on particularly lean mixtures. 
     The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.