Internal-combustion engines – Burning by highly compressed air – Oil engine air preheated
Reexamination Certificate
2000-06-20
2001-11-27
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Burning by highly compressed air
Oil engine air preheated
C123S525000, C123S578000, C123S464000
Reexamination Certificate
active
06321694
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to internal-combustion engines designed to operate selectively with gasoline and gas (for example, methane or LPG), of the type comprising a gasoline-supply system comprising a plurality of electronically controlled gasoline injectors, each of which is associated to one of the cylinders of the engine, a gas-supply system comprising a plurality of electronically controlled gas injectors, each of which is also associated to one of the cylinders of the engine, and electronic means for controlling the gasoline injectors and gas injectors.
The present applicant has already studied and proposed various solutions for internal-combustion engines of the type specified above (see, for example the European patent No. 0801223).
The purpose of the present invention is to provide a process for controlling an internal-combustion engine of the type specified above, which enables prevention of the drawbacks that occur with the engines so far built during the fuel-switching phase, i.e., during switching from gasoline supply to gas supply, or, vice versa, from gas supply to gasoline supply.
One first drawback that occurs during the said switching phase in engines according to the known art is represented by the considerable thermal stresses to which the catalytic converter provided in the engine-exhaust system is subjected on account of the undesired fluctuations in the metering of fuel during the phase of transition from one fuel to the other.
A further drawback that arises in known systems is represented by the possibility that inhomogeneities may occur in the delivery of the torque during the above-mentioned switching phase, with consequent problems from the standpoint of proper drivability of the vehicle.
The problems mentioned above derive from the fact that when the engine is switched from gasoline operation to gas operation, or vice versa, an initial transient phase occurs in which there is a joint presence of the two fuels in the cylinders of the engine. The simultaneous presence in the combustion chambers of the cylinders of the three components air, gasoline and gas gives rise to anomalies in the creation of the mixture. These problems are increased by the different state (liquid and gas) of the two fuels. In particular, in operation of the engine under normal running conditions with gasoline supply, a film of gasoline is deposited on the walls of the fuel supply pipes, the presence of which is important for proper operation of the engine. Vice versa, in operation of the engine with gas supply, proper filling of the combustion chamber is always guaranteed by the volatility of the fuel used. Switching from gasoline supply to gas supply, or vice versa from gas supply to gasoline supply, thus entails additional problems. The drawbacks that derive therefrom in the engines according to the known art are such as to force the adoption, in certain cases, of drastic solutions consisting in allowing the switching operation only when the vehicle is stationary, so as to prevent any possible problem from arising in driving on account of any loss of torque following upon fuel switching when the vehicle is travelling.
SUMMARY OF THE INVENTION
With a view to overcoming all the above problems, the subject of the invention is a process for controlling the fuel-switching phase in an internal-combustion engine designed to operate selectively with gasoline and gas, of the type indicated at the beginning of the present description, characterized in that, whenever a command is issued for fuel switching by means of deactivation of one of the two fuel-supply systems and activation of the other fuel-supply system, the injectors of the fuel-supply system that has been activated are controlled during an initial phase in a different way as compared to the normal engine-running condition so as to compensate for the transient phenomena due to the change of fuel.
More in particular, in the event of switching from gas to gasoline during the aforesaid initial gasoline-operation phase, the gasoline injectors are kept open for a longer time than for the normal engine-running condition with the purpose of enabling fast formation of a deposit of a film of gasoline on the walls of the fuel-supply pipes, whereas, in the case of switching from gasoline to gas during the aforesaid initial phase, the gas injectors are kept open for a shorter time than for the normal engine-running condition until there is complete evaporation of the film of gasoline that has formed on the walls of the pipes in the course of the foregoing gasoline-operation phase.
Thanks to the above characteristics, a linear and uniform operation of the engine is achieved, with consequent good drivability of the vehicle during the fuel-switching phase, even though the vehicle is travelling.
A further problem that has led to the present invention is represented by the safeguarding of a number of components of the motor vehicle that would otherwise be subject to excessive stresses in the event of switching from gasoline supply to gas supply. For instance, in the case of gas systems equipped with a pressure regulator heated by the engine coolant, for temperatures at engine starting in the region of −25 to −30° C., freezing of the coolant in the heating circuit of the pressure regulator could occur, so that operation would no longer be guaranteed, and the pressure regulator itself could get permanently damaged on account of the thermal stresses involved.
With a view to overcoming such a problem, in the preferred embodiment the process according to the invention is further characterized in that, during engine operation, the temperature of at least one predetermined component of the engine is estimated on the basis of a corresponding thermodynamic model, and operation with gas supply is inhibited when the said estimated temperature is outside a pre-determined range of acceptability.
Of course, another subject of the invention is an internal-combustion engine designed to operate selectively with gas or gasoline, of the type specified at the beginning of the present description and characterized in that the aforesaid electronic control means are programmed in such a way as to provide the control process described above.
The above-mentioned electronic control means may consist of two electronic control units, one of which is dedicated to controlling the gasoline-supply system, and the other is dedicated to controlling the methane-supply system, or else may consist of a single electronic control unit which is able to manage both fuel-supply systems.
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Ferrera Massimo
Miletto Giuseppe
Vergine Irene
C.R.F. Societa Consortile per Azioni
Huynh Hai
Sughrue Mion Zinn Macpeak & Seas, PLLC
Wolfe Willis R.
LandOfFree
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