Abstract:
A device and a method for detecting phase in four-stroke engines, in which an electronic control unit (ECU) detects a spark current as a measuring signal and determines whether ignition occurred for ascertaining the compression cycles of the cylinders, whereby the electronic control unit is able to cause the injection to be performed in a correct phase relation.

Description:
TECHNICAL OBJECTIVE 
     FIELD OF THE INVENTION 
     The present invention concerns internal combustion engines that are controlled in open and closed loop by an ECU (electronic control unt), and if the injectors for engines are controlled electrically by the ECU, then it is necessary to determine the phase angle when starting the internal combustion engine. Phase detection for a four-stroke Otto spark ignition engine indicates whether the piston is in the compression cycle or in the exhaust cycle during the upward movement. 
     BACKGROUND INFORMATION 
     In known systems, this is achieved, for example, by an additional transmitter wheel on the camshaft, or by discharge (outflow) detection. 
     SUMMARY OF THE INVENTION 
     An exemplary method of the present invention is directed to a method used for detecting phase with the aid of an ionic-current measuring circuit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an overview of the entire system, including a cylinder, an ignition system, an arrangement or structure for measuring ionic current, an arrangement or structure for forming features and an electronic control unit (ECU). 
     FIG. 2 shows an exemplary embodiment according to the present invention. 
     FIG. 3 shows exemplary signal shapes. 
     FIG. 4 shows a flow chart for an exemplary method according to the present invention. 
    
    
     DESCRIPTION 
     The present method is presented in FIG. 1 on the basis of an exemplary embodiment. It utilizes arrangement or structure  3  for measuring ionic current, in that the ignition, system  2 , is observed with the aid of these arrangements the ignition system  2 , may by used to start combustion process  1 . 
     If an ignition spark develops at the spark plug, and if ionic current is measured at this spark plug during this time, then the spark current can be verified with the aid of arrangement or structure  3 . The detection of an ignition spark can be utilized for determining the phase. 
     According to Paschen&#39;s law, the greater the pressure between the electrodes, the higher the ignition voltage. If the engine is turned by the starter, then the gas in the combustion chamber is compressed after each 720° of crankshaft revolution. This pressure rise in the compressed gas, into which no fuel has yet been injected, leads to an increased ignition voltage. The difference between high and low ignition voltage can be determined by the ignition energy. If only so much energy is made available to the system that it suffices for ignition in the ranges of low pressure, but not in those of high pressure, then a distinguishing feature can be formed by analyzing the spark current. 
     If no ignition spark has sparked over, then only the primary and secondary leakage capacitance will be charged, and in the next step, the energy is fed back into the vehicle electrical system via the free-wheeling diode D located in the igniter or externally. A very brief ionic current will be measured which is simulated by the spark current. 
     The correct energy level is determined as follows: 
     Even before the starter begins with the rotation, the interrupting current, provided with sufficient signal-to-noise ratio, is determined by a series of ignition sparks, so that an ignition is reliably effected. This adjustment can possibly include  10  iterations. It is possible that several cylinders will already be in the compressed state. In this case, the necessary energy level is incorrectly determined. However, at least half the cylinders will be in a sufficiently non-compressed state, so that even in this case, sufficient redundancy is still provided. 
     Phase detection and ignition control are carried out continuously at all cylinders with the aid of the ionic-current measuring circuit. Following output ignition (following each output spark), if necessary, the ascertained characteristic value is acquired by the ECU and classified as successful (effected) or unsuccessful (not effected) ignition. If misfiring is detected, given sufficient ignition repetition frequency, a plurality of ignitions can be evaluated within the time period that a piston passes the compression top-dead-center, so that reliable information is obtained with respect to the cylinder distant by 360° of crankshaft revolution. That is to say, in the case of one cylinder, there is no ignition, and in the case of the cylinder distant by 360° of crankshaft revolution, the ignition spark continues. From this point on, the phase is known. 
     At the latest after one revolution, after running past the reference mark on the crankshaft transmitting wheel, it is possible to begin with injection at the correct cylinder. In this context, it is imperative that the interrupting current which is equal to the energy introduced into the coil) be maintained constant. In some instances, the battery voltage must be determined by the ECU and the dwell period/dwell angle be corrected. 
     Using an exemplary inductive ignition system, “feature” formation occurs as follows: 
     At any rate, the ionic-current measuring device can determine a part of the spark current, and is generally fully driven in this manner. If, after the energy level has been adjusted, an ignition attempt is carried out, the ionic current is integrated during the period of an ignition spark, the result is detected by a Sample &amp; Hold and is made available to the ECU. 
     Another exemplary embodiment for feature acquisition may be implemented in that the measured signal is low-pass filtered and observed with a peak-value acquisition device. The peak value is supplied to the ECU and is subsequently compared to a threshold. 
     FIG. 3 shows, by way of example, the signals occurring at the inductive ignition system. Differentiation is made between “unsuccessful (not effected) ignition” and“successful (effected) ignition”. Shown are: the secondary current which flows in L 2  (see FIG.  2 ); the ionic current which is measured by the ionic-current measuring device and, illustratively, the low-pass signal of the measured ionic current which is intended to show the feature formation. 
     It is assumed that the manner in which an inductive ignition system functions is sufficiently familiar. First of all, the ignition energy is introduced via the primary side into the ignition coil by closing the transistor. At point of time To, ignition transistor T is switched to highly-resistive and the energy in the coil now drives a current in the primary winding and secondary winding. The current in the secondary winding is designated as i sec , and can be seen in each case in the first diagram. 
     For unsuccessful ignition in which the energy in the ignition coil does not suffice for the ignition spark to spark over, the entire arrangement behaves like an LC oscillating circuit having one coil in the primary side and secondary side, respectively. The capacitances are produced in each case by leakage and component capacitances. On the secondary side, they are coil capacitance, cable capacitance and spark plug capacitance. If half the oscillation is past, the current in the primary side and secondary side becomes negative. At this point, on the primary side, free-wheeling diode D begins to conduct and feeds the remainder of the energy back into the battery. The energy is withdrawn in this way on the secondary side as well, and the current flow is brought quickly to a standstill. Since the ionic currents are very small, the signal level of the ionic-current measurement i ion  is immediately driven (modulated) to a maximum. If ionic-current signal i ion  is low-pass filtered TP{i ion }, then only a low signal level is achieved. 
     Successful ignition, in which there is a spaarkover before the leakage capacitances have been charged with the entire energy, the triangular spark current, typical for an inductive ignition system, flows in the secondary side. This, in turn, is sufficient to fully modulate (drive) the level of the ionic-current measuring device. Low-pass filtered ionic-current signal TP{i ion } achieves a perceptibly higher level then the signal in the case of an unsuccessful ignition. 
     The ECU can easily distinguish the two cases. 
     The exemplary method of the flow chart shown in a FIG. 4 is applicable for all or appropriately selected cylinders which are to be observed for phase detection. For an engine having a high number of cylinders, all the cylinders will probably not be necessary for detecting phase. This exemplary flow chart is intended to provide a simpler view of the exemplary method. 
     Thus, the exemplary embodiments involve measuring ionic-current for observing ignition sparks and the phase detection derived therefrom. 
     If ionic-current measurement is provided on a vehicle it is believed that phase detection can be installed by a small additional technical expenditure. 
     Since the exemplary method is supported by already existing resources, of is belied to be extremely cost-effective.