Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
1999-10-21
2001-07-03
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S527000, C123S687000
Reexamination Certificate
active
06253751
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for fuel proportioning in a gas-powered combustion engine. It also relates to a device for such fuel pro portioning.
Gas intended for driving a gas engine is usually stored at high pressure. After pressure reduction in one or more stages, the as 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 filling stations. 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 filling stations 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 excess air, 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 &lgr; probe which is usually employed for gasoline engines to aim at a value of about 1.0, since what is required is a different type of &lgr; probe which can monitor higher &lgr; values. As such &lgr; 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 &lgr; 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.
SUMMARY 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.
These objects are achieved according to the invention by a method of fuel proportioning for a gas powered combustion engine which includes: mixing gas after reduction thereof with air to form a gas/air mixture and supplying the gas/air mixture to the engine; monitoring a parameter in the engine exhaust which is related to the proportion of air and gas in the mixture; and when the value of the parameter deviates from a set-value, if at essentially the same time the engine is operating in a predetermined situation, adjusting the value of the parameter back to its set-value by adjusting the pressure level brought about by the pressure reduction. 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 includes: a pressure regulator for reducing the pressure of gas supplied thereto; a mixer arranged after the pressure regulator for receiving the reduced pressure gas from the pressure regulator and mixing the reduced pressure gas with air to form a gas/air mixture; an exhaust sensor arranged in the outlet of the engine; a control unit connected to the exhaust sensor for resetting the proportion of the gas/air mixture as a function of an output signal from the exhaust sensor; and at least one operating sensor connected to the control unit for indicating the operating state of the engine. The control unit is connected to an actuator coupled to the pressure regulator and is arranged to activate the actuator when the value of the output signal from the exhaust sensor deviates from a predetermined set-value, if at essentially the same time the operating sensor indicates that a predetermined operating situation prevails, to adjust the pressure level of the reduced pressure gas to reset the output signal from the exhaust sensor to the predetermined set-value thereof. 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 &lgr; probe for measuring &lgr; values greater than 1.0. Further features and advantages of the invention are indicated by the following detailed description and patent claims.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.
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Argenbright Tony M.
Ostrolenk Faber Gerb & Soffen, LLP
Scania CV Aktiebolag
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