METHOD AND DEVICE FOR FUEL PROPORTIONING IN A GAS-POWERED COMBUSTION ENGINE

Abstract: Fuel proportioning in a gas-powered combustion engine is effected so that when the value of a parameter monitored in the exhaust gases deviates from a set-value, the level of the gas input pressure to a mixer for gas and air is adjusted in a specified operating situation so that said set-value is reverted to. A device for fuel proportioning includes a pressure regulator (3) whereby the outlet pressure can be adjusted automatically during a specified operating situation by means of a control unit (11). After adjustment has been carried out, the setting reached is maintained for a lengthy period.

Description: Method and device for fuel proportioning in a gas-powered combustion engine Technical area The invention relates to a method for fuel proportioning in a gas-powered combustion engine in accordance with the preamble to patent claim 1. It also relates to a device for such fuel proportioning, in accordance with the preamble to patent claim 4. State of the art Gas intended for driving a gas engine is usually stored at high pressure. After pressure reduction in one or more stages, the gas is mixed with air in correct proportions for good combustion. A larger or smaller quantity of gas and air is supplied, depending on the load. Mixing of gas and air usually takes place in a mechanical type of mixer which has to be set for the particular quality of gas by applying a manual basic setting for maintaining the intended ratio between gas and air during load variation. When steady conditions prevail, the desired good combustion result is achieved, but if the gas proportion changes, e.g. because of pressure change, gas quality change or any other reason, an adjustment is required to restore the correct proportions of gas and air and hence achieve the intended good combustion. A need for adjustment of this kind may arise, for example, from refuelling. There have also been found to be relatively large differences in the quality of gas fuel available in different geographical areas. This means that the manufacture of gas engines has to include individual adaptation of each engine according to the market or geographical area for which it is intended. The way gas engines are often used means that they are always refuelled from the same depot. In such cases it is sufficient, at least for a certain time, to abide by the manufacturer's original setting, but the fact that without adjustment the engine cannot be used in other geographical areas or use fuel from other fuel depots does of course limit the possibilities of using such an engine in, for example, a vehicle intended to travel considerable distances. From the operating point of view it would be a great advantage if adjustment could be effected automatically. This would not only mean that any carelessness or forgetfulness on the occasion of refuelling need not cause bad combustion but also that a difficult operation could be obviated. It would thus be easier for gas-powered vehicles to use fuel from different filling stations, thereby facilitating lengthy journeys. Like a diesel engine, a gas-powered combustion engine usually operates with air excess, i.e. with an air/fuel ratio greater than 1.0. This means that the oxygen content of the exhaust gases cannot be measured by means of the conventional type of λ probe which is usually employed for gasoline engines to aim at a λ value of about 1.0, since what is required is a different type of λ probe which can monitor higher λ values. As such λ probes have now reached the market, various designs have been proposed whereby continuous adaptation and correction of the air/fuel ratio takes place in the actual mixer on the basis of signals from the λ sensor. Also known is the use of electronically controlled gas injection whereby a control unit calculates and proportions the required gas quantity on the basis of various operating data. A disadvantage of these solutions is that they are relatively sensitive and require a great deal of maintenance. Objects of the invention One object of the invention is to use simple means to make simple and reliable and yet precise fuel proportioning possible in a gas-powered combustion engine in varying external conditions. Further objects are to maintain good reliability of a mechanical gas mixer and achieve at moderate cost stable emission and torque levels. Brief description of the invention These objects are achieved according to the invention by a method of fuel proportioning as indicated in the characterising part of patent claim 1. According to an advantageous embodiment of the invention it is appropriate to use the air/fuel ratio as the parameter monitored in the engine's exhaust gases and to carry out adjustment at full load and within a limited engine speed range. Effecting adjustment in this manner makes it possible to limit the need for adjustment so that it need only be effected relatively infrequently. Adjustment being also carried out automatically by means of suitable equipment achieves good operating results. A device proposed according to the invention for fuel proportioning in a gas-powered combustion engine is implemented, according to the invention, in accordance with the characterising part of patent claim 4. Such a device makes it possible to use a conventional mechanical gas mixer, with the latter' s accompanying advantages. Moreover, only relatively infrequently does the device proposed according to the invention need to come into action. The exhaust sensor used is advantageously a λ probe for measuring λ values greater than 1.0. Further features and advantages of the invention are indicated by the following detailed description and patent claims. Description of diagrams The invention is explained in more detail below by means of an embodiment depicted in the drawings, in which: Fig. 1 shows schematically a device implemented according to the invention for fuel proportioning in a gas-powered combustion engine, Fig. 2 shows an end view of a settable pressure controller for the device in Fig. 1, and Fig. 3 shows a section III-III in Fig. 2. Description of an embodiment A device 1 implemented according to the invention for fuel proportioning includes a first gas line 2 via which gas at a certain pressure is led from a gas source (not depicted in detail) in the form of a gas tank into a gas regulator 3 for pressure reduction. From the gas regulator 3 the gas then proceeds at reduced pressure via another line 4 to a mixer 5 in which the incoming gas is mixed with air which is supplied via a third line 6. The resulting proportions of air and gas are such that the air/gas ratio λ has a value exceeding 1.0, i.e. a lean mixture. From the mixer 5 the mixture of gas and air is led via a line 7 to a combustion engine 8 in which the mixture is burnt before leaving the engine 8 via an exhaust line 9 in order gradually to be led out, possibly via a catalyst, to the surrounding atmosphere. In the exhaust line 9 there is close to the engine an exhaust sensor 10 to detect the value of a parameter of the exhaust gases, here a λ probe for detecting the λ value or oxygen content of the exhaust gases. In this example the combustion engine takes the form of a piston type of engine intended for gas operation and is intended to be used as the drive engine in a vehicle, e.g. a heavy-duty bus. A control unit 11 is connected via a line 12 to the exhaust sensor 10 and via a line 13 to an operating sensor 14 for detecting the operating conditions in which the engine 8 is operating. The operating sensor 14 is mounted on the mixer 5 and is arranged to detect the rotational position of the latter' s throttle shaft (not depicted). The operating sensor 14 can thus detect whether the engine 8 is, for example, running at full load or not. In alterative embodiments other ways of detecting whether the engine is running at full load may be used. The control unit 11 controls via a line 15 an actuator 16 which via a control device 17 can act upon the pressure regulator 3 in order to reset the latter' s outlet pressure. In addition to the operating sensor 14 mounted on the mixer 5 to detect the engine's operating state, there is also a sensor 18 which is mounted directly on the engine 8 and is connected via a line 19 to the control unit 11. This sensor 18 is a speed sensor which detects the speed of the engine. Together with the sensor 14, it thus detects the engine's prevailing operating situation. The mixer 5 takes the form of a mechanical type of mixer, e.g. of IMPCO ® make type 200D, intended for use in engines. The pressure regulator 3 takes the form of a pressure regulator provided with setting facilities, e.g. of IMPCO ® make, type T-PEV-1. Such a pressure regulator 3 is depicted in more detail in Figures 2 and 3. This pressure regulator has a housing 20 into which gas at a certain pressure is supplied via an inlet 21 and out of which the gas flows at a lower pressure via an outlet 22. An adjusting spring 23 for adjusting the ratio between the inlet and outlet pressures is arranged in the housing 20. The housing 20 is usually provided with an adjusting screw which can be acted upon manually to alter the tension of the adjusting spring 23. In the embodiment depicted here, however, the adjusting screw is replaced by the actuator 16 and the control device 17 whereby the actuator 16 can move the control device 17 in either direction represented by the double-headed arrow 24 to alter the tension in the adjusting spring 23 and hence alter the outlet pressure. The actuator 16 may advantageously be mounted on the pressure regulator 3 but may of course also be fastened elsewhere, e.g. directly to the engine, provided that its distance from the housing 20 is well defined. Instead of the mixer and pressure regulator indicated above it is of course possible to use other similar types of mixer and pressure regulator. In normal steady operating conditions the mixer 5 brings about desired proportions of air and gas so that the engine can be operated at a predetermined air/fuel ratio which is controlled and monitored by means of the exhaust sensor 10. Changes in ambient temperature and in gas quality, which may for example arise from refuelling, may cause a change in the λ value. Wear in the mixer 5 may also possibly alter the λ value, thereby affecting the engine's emission level and torque. According to the invention, it is possible, while the engine continues to operate, for the outlet pressure from the gas regulator 3 to be automatically adjusted as necessary for monitoring and correcting a λ value change. This is achieved automatically by the control unit 11 activating the actuator for a long enough time to make the control device 17 reset the pressure regulator to a pressure which results in the desired λ value represented by a predetermined output voltage from the λ probe 10. Gas pressure adjustment is advantageously carried out according to the invention when the engine is operating at full load, which is indicated by the sensor 14 on the throttle shaft and, within a certain engine speed range, indirectly by the sensor 18. Adjustment at full load will result in correct resetting in the worst operating situation, which is when correct adjustment is most critical. It is also possible to use a differently defined operating situation. After adjustment has been effected and the desired set-value for λ has again been reached, the engine is run conventionally with the pressure regulator setting constant and unchanged until a further adjustment becomes necessary, e.g. because of a change of gas quality arising from refuelling. Adjustment thus takes place relatively infrequently and normally required changes in fuel quantity are catered for by the driver by means of the mechanical mixer 5. The fact that adjustment takes place during operation ensures good combustion and a stable emission level.

Claims: Patent claims 1. Method for fuel proportioning in a gas-powered combustion engine whereby gas, after pressure reduction, is mixed with air and supplied to the engine as a function of the prevailing load, and whereby the value of a parameter monitored in the engine exhaust gases is used for acting upon the fuel proportioning, characterised in that when the value of the parameter monitored in the exhaust gases deviates from a predetermined set-value, the value of that parameter is adjusted back to its set- value by the pressure level brought about by the pressure reduction being adjusted while the engine is operating in a predetermined operating situation which is intended for adjustment, and that fuel proportioning thereafter takes place at the adjusted pressure level. 2. Method according to claim 1 , characterised in that the λ value is used as the parameter monitored in the engine's exhaust gases. 3. Method according to claims 1 and 2, characterised in that the adjustment takes place at full load. 4. Device for fuel proportioning in a gas-powered combustion engine for vehicles, with a pressure regulator (3) for reducing the pressure of gas supplied, with a mixer (5) which is arranged after the pressure regulator and by means of which gas is mixed with air and supplied to the engine as a function of the prevailing load, with an exhaust sensor (10) which is arranged in the outlet (9) of the engine (8) and is connected to a control unit (11) for resetting the fuel proportioning as a function of the exhaust sensor's output signal, and with at least one operating sensor (14) which is connected to the control unit (11) and indicates the operating state of the engine, characterised in that the control unit (11) is connected to an actuator (16) coupled to the pressure regulator (3) in order to reset the output pressure from the pressure regulator, that the control unit (11) is arranged to activate the actuator (16) when the value of the output signal from the exhaust sensor (11) deviates from a predetermined set-value and when, at the same time, the operating sensor (14) indicates that a predetermined operating situation prevails, and that the control unit (11) is arranged to respond to the reaching of a set-value for the output signal from the exhaust sensor (10) by deactivating the actuator (16) in order to maintain the setting position reached. 5. Device according to claim 4, characterised in that the exhaust sensor (10) is a λ probe for measuring λ values greater than 1.0. 6. Device according to claim 4 or 5, characterised in that the operating sensor (14) is a sensor for indicating a predetermined operating situation in the form of full load. 7. Device according to claim 6, characterised in that the operating sensor (14) is a sensor which is coupled to the engine's throttle shaft and arranged to detect the latter' s full load position. 8. Device according to any one of claims 4-7, characterised in that the control unit (11) is connected to a speed sensor (18) arranged on the engine for indicating the engine's operating state.

Inventors: CARLSSON GOERAN, CARLSSON, GOERAN
Applicants: CARLSSON GOERAN, SCANIA CV ABP, CARLSSON, GOERAN, SCANIA CV AKTIEBOLAG (PUBL)
Application year: 1998
Main classification: F02M21
IPC codes: F02D19, F02M21