Internal-combustion engines – Charge forming device – Gaseous fuel and air mixer
Reexamination Certificate
2001-11-26
2003-06-17
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Charge forming device
Gaseous fuel and air mixer
Reexamination Certificate
active
06578560
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to gas injection systems, particularly of methane, for internal combustion engines, for the type comprising:
a plurality of electromagnetically controlled injectors associated to the various cylinders of the engine,
a distributing manifold, or rail, communicating with said injectors,
a reservoir feeding the distributing manifold, where the pressurised gas is accumulated,
a pressure regulating valve interposed in the connection between the reservoir and said distributing manifold, and
an electronic control unit set up to control the injectors and to control the opening time to meter the amount of gas injected in each cylinder according to the operating conditions of the engine.
Methane injection systems of the type indicated above have been recently proposed to replace more traditional systems which employ distributing devices to meter the methane to be mixed with the air feeding the engine, according to an arrangement which is similar to that of a normal gasoline carburettor. These more traditional solutions are not acceptable because they are not suitable for working in conjunction with an engine electronic control system which particularly is capable of controlling metering according to the composition of the exhaust gas detected by a lambda sensor. For this reason, the applicant has previously proposed (see European Patent EP 0 801 223) a methane injection system for internal combustion engines comprising a plurality of electromagnetically controlled injectors which are activated by an electronic control unit in order to meter the amount of gas injected in each cylinder according to the operative conditions of the engine.
In the methane electronic injection systems proposed to date, methane metering in the engine cylinders is obtained by varying the opening time of the injectors according to the various operative parameters of the engine, such as the position of the accelerator pedal, the speed of revolution of the engine, the ambient temperature, the altitude (which effects the amount of air taken in by the engine), etc. The opening time of the injectors is the only parameter which can be used to control methane metering, because the pressure of the methane in the distributing manifold is essentially constant.
Furthermore, in said known systems, the pressure regulating valve interposed between the methane reservoir and the distributing manifold essentially consists of a self-standing component, comprising a restricted passage and a membrane mechanism which regulates said passage. However, the systems configured in such a fashion were not satisfying in transient ratios of engine operation. Specifically, the systems are not capable of holding pressure downstream to the valve at a predefined value, which is essentially constant in the case of dynamic variations in the flow of methane, such as, for example, in the case of abrupt engine acceleration. Moreover, the systems are capable of working at a single predefined pressure value to be created in the distributing manifold. In actual fact, the engine operation presents a very high load dynamics which originates methane load variations, also for ratios in the range of 1:30 or 1:40. The pressure regulating valve is usually designed on the basis of a compromise between the existing needs in extreme conditions of load of the engine. This is because a pressure regulating valve with an excessively small passage may be optimal when the engine is idling but will not provide an adequately fast response when the engine load increases rapidly, such as in the case of abrupt acceleration. Conversely, if the passage of the pressure regulating valve is relatively wide, the system will respond well to high engine loads but will not be capable of ensuring accurate metering at low loads.
SUMMARY OF THE INVENTION
The object of the invention is to obviate said shortcomings, making a system which is capable of ensuring accurate gas metering in all conditions of operation of the engine and particularly in the case of rapid variations of gas flow determined by abrupt variations of engine load.
In order to achieve this object, the system according to the invention is characterised with respect to the known systems principally in that in comprises means for regulating the pressure of the gas in the distributing manifold.
More precisely, said regulation means comprise:
an electromagnetic actuator controlling said pressure regulating valve,
a sensor of the pressure in the distributing manifold, suitable for sending an electrical signal indicative of said pressure to the electronic control unit,
a sensor of the pressure in the gas feeding line between the reservoir and the pressure regulating valve, suitable for sending a electrical signal indicative of said pressure to the electronic control unit,
memory means associated to said electronic control unit containing maps of the theoretical predetermined pressure values to be created in the distributing manifold according to the variation of the parameters of operation of the engine,
said electronic control unit being programmed to control the electromagnetic actuator of the pressure regulating valve according to the signals output by the sensors of the pressure in the distributing manifold and of the pressure in the line upstream to the pressure regulating valve, in order to obtain a pressure in the distributing manifold which is essentially equal to the theoretical predetermined value that the control unit retrieves in said memory means according to the value of one or more parameters of operation of the engine.
Thanks to the aforesaid characteristics, the system according to this invention is consequently capable of ensuring accurate metering of gas in the cylinders of the engine in any condition of operation of the engine. From a practical point of view, the variation of pressure in the distributing manifold can reach, for example, ratios in the order of 1:3 or higher, for example with a minimum pressure value essentially equal to 3 bars and a maximum value equal to approximately 9 bars. Thanks to the possibility of regulating the pressure value in the distributing manifold, the system is capable of optimally managing any static or dynamic condition of operation of the engine.
Said pressure regulating valve according to the invention has a valve seat and a lock pin moveable between a closed position, in which the lock pin is in contact with the valve seat, and an open condition, in which a restriction is formed between the lock pin and the valve seat putting an inlet opening communicating with the line from the reservoir into communication with an outlet opening communicating with the line leading from the distributing manifold. An important characteristic of the invention is in that said control unit is set up to control a periodical switching of the pressure regulating valve between said closed and open conditions, at a predefined frequency. In other words, alternatively to progressively and continuously varying the passage of the pressure regulating valve according to the electrical control signal sent hereto, the regulation of the pressure in the distributing manifold can also be obtained by opening and closing the valve at a constant frequency. In this case, the regulation of the valve is obtained by varying the duty cycle of the valve, i.e. by varying the ratio between opening time and total period in each opening and closing cycle of the valve according to the pressure upstream and downstream to the valve and according to the conditions of operation of the engine, and particularly to the conditions of static and dynamic load of the engine.
According to an additional characteristic of the invention, said predefined frequency is chosen essentially equal to the frequency at which any injector in the system is activated. The opening of the pressure regulating valve is synchronous and timed in advance with respect to the activation of the injectors, so that said valve opens before each activation of any injection in the system. In this way, the pressu
Argenbright Tony M.
Benton Jason
CRF Societa Consortile per Azioni
Sughrue & Mion, PLLC
LandOfFree
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