CYLINDER RECOGNITION APPARATUS FOR A DISTRIBUTORLESS IGNITION SYSTEM

Abstract: A distributorless ignition system using a dual-spark ignition coil generates a signal indicative of which of the two cylinders associated with the dual-spark coil is operating in its power stroke by means of a single detector (15) connected to a predetermined one of the cylinders. The output of the detector is fed to a sample and hold circuit (21) which supplies the peak value from the detector to the control unit (10) of the ignition system where the peak value is evaluated and identified as indicating that the predetermined cylinder is in its power stroke when the detected peak value signal is at its higher level. Conversely, when the peak value signal is at its lower level the control unit determines that it is the other of the two cylinders which is in its power stroke and signals this accordingly.

Description: Cylinder Recognition Apparatus for a Distributorless Ignition System The present invention relates to a distributorless ignition system for an internal combus¬ tion engine and more particularly to an apparatus for generating signals for identifying in which cylinder of the engine an ignition event is occurring. Distributorless ignition systems for internal combustion engines are already known. These systems dispense with mechanical (rotary) distribution of the high tensions sparks and are usually used in combina- tion with other electronic open or closed loop systems such as fuel injection systems where a timing signal is required for controlling the operation of a fuel injec¬ tion system to sequentially inject fuel for each cylin¬ der in synchronism with the rotation of the engine. In one type of distributorless ignition system, the dis¬ tribution of high-voltage pulses is accomplished stati¬ cally by selective triggering of ignition coils, each of which produces two high-voltage sparks simulta¬ neously. One spark acts during the power stroke of one cylinder and the other spark acts during the exhaust stroke of another cylinder. With this type of static distribution, there exists the need to detect the cylinder which is in its power stroke. One way of carrying out the detection electronically is disclosed in EP-A-177145 where the two simultaneous sparks are both detected and the voltage levels of the detection signals directly com¬ pare in a gated comparator. The output of the comparator is used to control a monostable multivibrator which generates a pulse when an ignition event occurs in a selected one of the two cylinders involved. No pulse is generated at the output of the monostable multivibrator when an ignition event occurs in the other of the two cylinders involved. The disadvantage of this prior arrangement is that two detectors and a considerable amount of cir¬ cuitry are required and it is still necessary to logi¬ cally process the gating signal to the comparator and the output from the monostable multivibrator in order to determine in which of the two cylinders an ignition event has occurred. The present invention provides cylinder recognition apparatus for a distributorless ignition system comprising ignition control means for generating ignition signals, a signal distributor connected to the ignition control means and arranged to be connected to ignition coils associated with two cylinders, detection means for generating a signal indicative of spark generation in a cylinder of an internal combustion engine, processing means for processing the signal generated by the detection means, and control circuit responsive to the processing means for outputting a control signal indicative of the cylinder which is operating in the power stroke of the cycle of the engine, characterised in that the detection means comprises a single detector for detecting the output pulse from the signal distributor to one of the two cylinders of the engine, in that the processing means comprises a circuit for generating a signal representing the peak amplitude of the signal generated by the detection means, and in that there is further provided means for evaluating the magnitude of the peak amplitude detected by the peak value circuit to determine whether said one of the two predetermined cylinders is in a power or exhaust stroke condition. An advantage of the present invention is that it simplifies the circuitry as compared with that disclosed in EP 177,145 and only requires the use of one detector. Features and advantages of the present inven¬ tion will be more readily understood from the following description of an embodiment thereof given by way of example with reference to the accompanying drawings, in which:- Fig. 1 shows diagrammatically a distributorless ignition system; Fig.' " 2 shows a block diagram of part of the electrical circuitry shown in Fig. 1 and incorporating the present invention; and Fig. 3 shows a circuit diagram of part of the block diagram shown in Fig. 2.. One form of distributorless ignition system is shown diagrammatically in Fig. 1 connected to an engine which is itself shown in end view so that only one of the four cylinders of the engine is in fact visible. In Figure 1 , the distributorless ignition system comprises a control unit 10 which receives engine speed and reference signals from the sensor 11 and generates control signal via a control line 12 to a static high-voltage distributor 13. The distributor 13 includes two power output stages and two ignition coils (14). Each of the output stages comprise an ignition coil and each end of the ignition coil is connected to a respective spark plug such that when an ignition coil is operated a high-voltage output are generated which cause two sparks of-different polarity to be generated simultaneously in the spark plugs associated with the ognition coil. Turning now to Figure 2 which shows a block diagram of a representation of a part of the ignition system shown in Figure 1 , the same reference numerals are used for the same parts for convenience. In this arrangement, an inductive detector 15 is provided for sensing the voltage in the high-voltage line 16 between one end of the high-voltage output of one of the igni- tion coils 14 and a spark plug. It is to be noted that the other high-voltage line from the ignition coil 14 to the other spark plug is not provided with a detec¬ tor. The reason for this will be explained in more detail below. The signal from the detector 15 is fed via a line 19 to a pulse shaper circuit 20 and thence to a peak value detection circuit in the form of a sample and hold circuit 21. The output of the sample and hold circuit is fed via a line 22 to the control unit 10. The pulse shaper and sample and hold circuit are shown in more detail in Fig. 3 where again the same reference numerals are used for the same parts. From Figure 3, it will be seen that the pulse shaper 20 comprises a simple diode capacitor resistor arrangement which overcomes the difficulties resulting from the fact that the signal on the line 19 exists for only a short period of time. Further the peak value detector is in the form of a series connected transistor T21 and capacitor C21. The transistor T21 also provides overvoltage protection. Since the signal to be measured has an extremely steep edge, the transistor T21 is selected so as to conduct current from its base to its collector as soon as the transistor reaches its saturated operating region. A transistor T22 is connected in parallel with the capacitor C21 and operated via a control signal from the control unit 10 on its output line 12. The transistor T21 has the single function of re-setting the peak value detection circuit 21 to zero by an other ignition output after the A/D conversion of the potential output on line 22. Alternatively, it is possible for a special control signal to be sent to the transistor T22 after the value fed by the sample and hold circuit 21 to the control unit has been evaluated by an analog to digital converter associated with the control unit 10. In the operation of the type of distributorless ignition system described above, two sparks are generated by the ignition coil in response to a single control signal from the control unit 10 on the output line 12. Consequently, for any one cylinder spark flashovers are generated twice every four stroke cycle of the cylinder i.e. alternately during the exhaust stroke and during the transition between the compression stroke and the power stroke. In general, the breakdown voltage is much less during the exhaust stroke than during the compression/power stroke due to the difference in pressure in the cylinder. For this reason, two successive analog to digital-converted peak values from the sample and hold circμit 21 are presented to the microprocessor in the control unit 10. The processor recognises that the higher peak value indicates that the cylinder in question is in its compression/power stroke and can trigger ancillary control equipment e.g. fuel injection equipment accord¬ ingly. Equally, it recognises the lower peak value signal as indicating that the other cylinder is in its compression/power stroke and again can react accord¬ ingly. However, this basic assumption of cylinder condition is not unambiguous for all operating condi¬ tions of the engine since the amplitude allocation can reverse in some operational conditions such as, for example, over-run. For this reason, the control unit is arranged to operate in the above manner only in unambiguous operating conditions such as, for example, full or part load or idling. In special cases which can be encountered and in which starting does not take place at normal crank- -r ing speeds but at high engine speeds e.g. during down¬ hill running in the over-run phase, parallel injection of fuel into the cylinders is first used rather than sequential injection. When changing from over-run to part load, the system is then synchronised as described above. Various modifications may be made to the above described circuitry. The detector 15 may by a capacitive detector rather than an inductive detector. Further, ignition systems using dual-spark and four- spark coils require two separate power output stages. The engine speed and reference signal generator deter¬ mines which of the two output stages is triggered at a given time.

Claims: CLAIMS : 1. Cylinder recognition apparatus for a distributorless ignition system comprising ignition control means (10) for generating ignition signals, a signal distributor (13, 14) connected to the ignition control means (10) and arranged to be connected to ignition coils associated with two cylinders, detection means (15) for generating a signal indicative of spark generation in a cylinder of an internal combustion engine, processing means (20, 21 ) for processing the signal generated by the detection means (15), and control circuitry (10) responsive to the processing means for outputing a control signal indicative of the cylinder which is operating in the power stroke of the cycle of the engine, characterised in that the detec- tion means comprises a single detector (15) for detect¬ ing the output pulse from the signal distributor to one of the two cylinders of the engine, in that the processing means comprises a circuit (21 ) for generating a signal representing the peak amplitude of the signal generated by the detection means, and in that there is further provided means for evaluating the magnitude of the peak amplitude detected by the peak • value circuit (21 ) to determine whether said one of the two predetermined cylinders is in a power or exhaust stroke condition. 2. Apparatus according to claim 1 , wherein the peak value circuit comprises a sample and hold cir¬ cuit. - 3. Apparatus according to claim 1 or 2, and comprising means for generating a reset signal for resetting the peak amplitude circuit (21). 4. Apparatus according to claim 1, 2 or 3, wherein the processing means further comprises a pulse shaping circuit (20) for shaping the output- of the detection means (15), the pulse shaping circuit (20) being connected to the input to the peak amplitude circuit (21 ) . 5. Apparatus according to anyone of the preced¬ ing claims, wherein the detection means is an inductive detection device.

Inventors: KLOETZNER WINFRIED, KRAUTER IMMANUEL, KLOETZNER, WINFRIED, KRAUTER, IMMANUEL
Applicants: BOSCH GMBH ROBERT, ROBERT BOSCH GMBH
Application year: 1988
Main classification: F02P15
IPC codes: F02D41, F02P3, F02P7, F02P15, F02P17