Control system and method for transmitting sensor signals for a combustion engine

TECHNICAL FIELD This invention relates to combustion engine and control system, comprising a number of cylinders within said engine, at least one ignition circuit for each cylinder, at least one combustion control unit for controlling said engine, a sensor device and a sensor control unit for supplying control signals to said combustion control unit.

PRIOR ART

This invention relates to optimisation of combustion engines, and especially large combustion engines, for instance such engines powered by natural gas. Prior art problems, related to such engines, will in the following be described for gas pumping machines, for pumping natural gas in large pipelines, but it is understood that the invention is not limited to gas pumping machines. The kind of gas pumping arrangement that has been used for many decades is in the form of a very large pump mechanism that is powered by a combustion engine using the natural gas that is being pumped for the combustion. Since the machines are very large they are also very costly. Accordingly there is a strive to keep these machines running as long time as possible. From this perspective it is important to try to power the pump arrangements in a controlled manner that minimizes wear and stress on the equipment. Moreover there is of course a desire to try to run the engines as efficient as possible, e.g. to keep emissions at a low, acceptable level. Many different attempts have therefore been used to optimize this machines. As a way of example the combustion of the engines have for a while been controlled by means of pressure transducers that detect the pressure within the combustion chamber of the engine.

However, firstly pressured transducers are relatively costly and have a limited lifetime. Furthermore the pressure within the combustion chamber does not provide sufficient information to be able to optimize the combustion within the combustion chamber.

Hence, further detectors are normally needed and with an increased amount of detectors cost and complexity also increases.

Ion sensing is a control concept that has been successfully used to optimize combustion within different kind of combustion engines, e.g. in personal vehicles. Tests have been performed to try to use this ion sense concept also on gas pumping machines. However, these test have failed since these large kind of gas pumping arrangements present

specific problems and specific needs that make known kind of ion sense technology inappropriate, i.e. cannot meet demands in relation to output and/or cost. For instance, due to the size of the machines and the low frequency of the engines no traditional concept can be used to produce desired result, but supplementary hardware will be needed in a form of signal enhancers, etc. A further complication is that there are extremely many different kinds of such natural gas combustion engines.

SUMMARY OF THE INVENTION

It is an object of the invention to eliminate or at least minimize the above problem, which is achieved by means of a combustion engine and control system, comprising a number of cylinders within said engine, at least one ignition circuit for each cylinder, at least one combustion control unit for controlling said engine, a sensor device and a sensor control unit for supplying control signals to said combustion control unit, wherein said sensor device includes an ion sensing device and wherein a current transmitting interface is used to transmit signals between said ion sensing device and said sensor control unit.

Thanks to the use of a current transmitting interface device the ion sensing technology may be efficiently implemented despite the difficulties that are associated with a natural gas combustion engine, by allowing the analogues signals from the ion sensors to be transmitted in an analogues form to a remote central control unit. Thanks to this arrangement the analogue signals may be transported considerable distances without any need of enhancement of the signals to enable efficient ignition, control, preferably by means of providing merely one central sensor control unit for the whole gas pumping machine. Further, in a preferred embodiment that interface may also be used to transmit control signals from the sensor control unit to each one of the ion sensing circuits, thereby presenting a very cost-efficient total system for optimised control of each combustion chamber, and especially by enabling the use of the same hardware despite type of engine.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in more detail with reference to the enclosed drawings, wherein:

Fig. 1 schematically presents a gas pumping arrangement according to the invention, Fig. 2 presents a schematic layout of a circuitry according to a preferred embodiment of the invention and,

Fig. 3 shows a diagram that presents the principles for a preferred mode of operating a control system according to the invention.

DETAILED DESCRIPTION In Fig. 1 there is shown a schematic view of gas pumping arrangement 1 according to the invention. The gas pumping arrangement 1 is a very large machinery used to pump natural gas in a pipeline 9. To power the pumps (not shown) there is a natural gas combustion engine, comprising a number of combustion units 2, i.e. combustion cylinders 2 that are powered by the natural gas being pumped (of course merely a fraction of the pumped amount of gas is needed for the pumping action). These machines may have from four up to 20 cylinders 2 and the space occupied by the machinery 1 may be very large, e.g. 9x3x2 m, i.e. huge machines. An ignition circuit 3, (in these kind of engines there may be several ignition circuits on each cylinder) comprising an ignition coil, a high tension lead and spark plug, is arranged together with each one of the cylinders 2. As indicated in Fig.l different control units 7, 7', 7" are normally used to control different parameters of the engine, e.g. a sensor control unit 7, an ignition control unit 7' and a fuel control unit 7", as is known per se. An ion sensing detector 5 is arranged in connection with, e.g. integrated with the ignition coil, each one of the ignition circuits 3. The ion sensing detection unit 5 transmits analogues data to the sensor control unit 7 by means of an interface 4 via cables 6. The sensor control unit 7 is arranged with at least one processing unit 8 for analyzing the signals from the ion sensing unit 3 and in its preferred mode, it is also arranged to supply control signals via the same interface 4 back to the ion sensing circuit 3. Thanks to the arrangement according the invention the sensor control unit 7 may continuously monitor and control the operating parameters of each combustion chamber 2 to facilitate optimized operation of the machinery 1, e.g. to deliver adequate signals for fuel and/or ignition control respectively.

In Fig. 2 there is shown a schematic view of elements of an ignition 3 circuitry and a control unit 7 (master) according to a preferred embodiment of the invention. There is presented an ignition circuit 3, e.g. including an ignition coil 30. Adjacent the ignition coil 30 there is arranged the ion current detector device 5, that receives signals 50 from the ignition coil 30, which is known per se and therefore not described in detail. The detector 5 supplies analogues voltage signals 51 to a 4-2OmA transmitter 40 (known per se) , including e.g. a transistor, resistor and amplifier, being powered by a continuous voltage supply 34 (e.g. 12v). In the transmitter 40 the voltage signals 51 are transformed into current signals and transmitted via a 4-2OmA interface/line 41. Cable/s 60, 61 are

arranged in between the transmitting end 41 of the interface unit 4 and a receiving end 42 arranged at/within the sensor control unit 7. Thanks to using current signals these cable/s 60, 61 may be very long and still supplying quality signals, e.g. 100:s of meters if needed. Together with the receiving end 42 of the interface unit there is a 4-2OmA receiver 43 (e.g. including a transistor and resistor (not shown)) that transforms the current signals to voltage signals. These transformed signals 71 are supplied to the processor 8. Hence, conversion of analogues signals from the ion sensor 5 into digital data, will occur within the control unit 7. The current signal will normally be allowed to pass through the receiver 43 and into a return cable 61 to ground 35 adjacent the ignition circuit 3. The processor 8 will enable analysis of the signals 71 and to enable adequate control of each cylinder 2 by supplying e.g. ignition control signals 81 to the ignition control unit T and/or fuel control signals 82 to the fuel control unit 7" (as a schematically indicated in Fig.l).

At the out put from the receiver 43, leading to the return cable 61, there is a transistor 70 that is normally closed, i.e. during reception of detection signals, for supply of sensor signals as described above. Accordingly, normally the transistor 70 is closed to enable transmission of analogues sensor signals from the ion sensing unit 5 to the sensor control unit. To transmit signals in the other direction the transistor 70, i.e. for serial communication from the sensor control unit 7 to the ignition circuit 3, the transistor 70 is used to initiate and transmit information to a serial to parallel conversion unit 32 (SPCU). First the transistor 70 initiates the SPCU 32 by sending pre-defined signals. This is achieved by rapidly opening and closing the transistor 70, since when the transistor 70 is closed the SPCU will "read" all signals between 4-20 mA as the same kind of signal, i.e. a 1 , whereas in its open state there will be no current to the SPCU 32 and therefore it will "read" this as a 0. Hence, when the transistor 70 has rapidly opened and closed a certain number of times according to a predefined pattern (which may vary), this will be detected by the SPCU 32 as a start of a serial transmission. Thereafter, by successive switching of the transistor 70 the master 7,8 can transmit a serial command to the ignition circuit 3 which changes operating conditions in the ion sense interface 5. By using a design according to the invention this multiplexing operation is easily achieved, since a very short time (e.g. l-4ms) is needed for supplying a "control package" 80, which in the shown example is transmitted back via the first cable 60.

In Fig. 3 there is shown an exemplary view of the mode of operation for supplying a serial command/"control package" 80 according to the invention. It is presented that

analogues data 71 from the ignition circuit 3 have been processed in the processor 8 of the sensor control unit 7 and has thereby identified that the ion sense interface 5 needs adjustment of one or more parameters to achieve optimized operation, e.g. the signals 51 being too low or too high to utilize the available range in an effective way. If so the analogues signals 71 will be used to provide control data 8B, 8D that are "packed into" a data string 80 containing synchronisation commands, 8A, 8C, whereby control of the ion sensing interface 5, may elegantly be achieved by the invention. Hence, the processor 9 will control the transistor 70 to open and close to produce data bits 8A-8D that will be transmitted from the sensor control unit 7 to the ignition circuit 3, including control signals 8B, 8D to adjust operating parameters of the ion sense unit 5 in the circuit 3. Upon receipt of the data package 80 at the receiving/processing unit 32 of the ignition circuit 3 these data bits will be accepted if the synchronisation commands 8 A, 8C fit a predetermined pattern. If so, control signals 33, based on the supplied data 8B, 8D, will be transmitted to adjust desired parameters of the ion sense circuit 5. When the data package 8A- 8D has been transmitted the transistor 70 will return to its closed position and the circuit arrangement 3, 4, 5, 6, 7 will enter into its sensing mode whereby again the ion sensing detector 5 will transmit analogous data 71 to the processor 8 of the control unit 7. This process will be continuously running to optimize the performance of each combustion unit 2. Thanks to the use of the serial command the same hardware may be used for different kind of combustion units/engines, emitting very different signals. Hence, the invention can drastically reduce maintenance, operating and control cost of any kind of natural gas combustion engine, in a very elegant manner.

The invention is not limited by the above description but maybe varied within the scope of the appended claims. For instance it is realized that the number of cylinders is of no relevance in performing control according to the invention. Moreover it is evident that it may also be used in connection with optimisation of other engines than engines powered by natural gas, e.g. diesel, gasoline, DME, methanol, ethanol hydrogen gas etc. Moreover, it is understood that all control units 7, T, 7" may be integrated into one and the same central, i.e. one single control unit. Further, in place of numerous return cables 61 it is possible to ground each ion sensing unit 3 directly in the engine (i.e. no need for any "local" ground cable 61 at all but instead for instance using a screw 61' (not shown) as ground device) and merely use one common ground cable from the engine to the ion sense control unit 7.