Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1990-11-29
1992-05-26
Wolfe, Willis R.
Internal-combustion engines
Charge forming device
Fuel injection system
123 25A, F02D 4104, F02M 2502
Patent
active
051157802
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a device for limiting the exhaust temperature in an internal combustion engine, comprising means for supplying a cooling medium to the combustion chamber of the engine.
BACKGROUND OF THE INVENTION
When designing modern internal combustion engines, especially supercharged engines, the exhaust temperature is an important parameter to be taken into consideration, due to firstly the relatively large gas flow in supercharged engines relative to the cylinder volume, secondly the higher exhaust counter-pressure when using catalytic exhaust converters leading to elevated exhaust temperatures, and thirdly the tendency to knock resulting from the desired to keep a relatively high compression ratio for preserving good engine suction characteristics.
A known method of limiting the maximum level of the exhaust gas temperature is to inject a cooling medium into the combustion chamber of the engine at those engine load conditions where there is risk that the temperature may exceed the maximum permissible level. Water can be used as a cooling medium injected into the combustion chamber through special injectors. The most common method is however to use extra fuel as a cooling medium and to quite simply use the ordinary engine injection system for making the engine fuel-air mixture richer.
Known systems for limiting exhaust gas temperature by injecting a cooling agent lack feedback circuits, and this means that one must assume a worst case situation when calculating the amount to be injected. The system must be designed with the assumption that the engine is operated with low octane fuel at high ambient temperature with maximum load and that these conditions shall prevail for a long period of time. This results in poor fuel economy since when driving normally even with a high load there is seldom any need to add extra fuel and temporary increases in load, such as when passing, do not bring the exhaust temperature to a critical value. Another disadvantage is that the exhaust gas temperature will be unnecessarily low when driving on high octane fuel at normal ambient temperature, and this results in a non-optimal fuel-air mixture ratio.
SUMMARY OF THE INVENTION
The purpose of the present invention is to provide a device of the type described by way of introduction which makes it possible to optimize the supply of cooling medium in such a manner that the medium is only supplied when there is actual need for cooling.
This is achieved according to the invention by means of a temperature-sensing means protruding into an exhaust-conducting conduit and which is coupled to a control unit for sending an exhaust gas temperature-dependent signal to the control unit, which in turn is coupled to said cooling medium-conducting means for controlling the supply of cooling medium as a function of the exhaust gas temperature.
The invention provides feedback or reaction control which makes it possible to optimize the engine for high octane fuel and normal driving conditions. When using supercharged engines, the gain will be lower fuel consumption under precisely those operating conditions where supercharged engines normally have very high fuel consumption.
The device according to the invention can be used to control injection of cooling medium in the form of fuel or water through a separate valve in the engine induction pipe, e.g. the start valve in an engine with fuel injection, but in a preferred embodiment for engines with fuel injection, the control unit is coupled to the fuel injection system to direct it to inject an excess of fuel through the ordinary injectors at exhaust gas temperatures above a certain level.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described below with reference to the accompanying drawings, where
FIG. 1 shows a block diagram of a preferred embodiment,
FIG. 2 shows a diagram illustrating the duty cycle of the control unit as a function of exhaust gas temperature,
FIG. 3 shows a diagram illustrating the shape of the pulse at several selected
REFERENCES:
patent: 4231333 (1980-11-01), Thatcher et al.
patent: 4389994 (1983-06-01), Denz et al.
patent: 4408585 (1983-10-01), Stuckas
patent: 4558665 (1985-12-01), Sandberg et al.
patent: 4561403 (1985-12-01), Oyama et al.
patent: 4671234 (1987-06-01), Tegtmeier
patent: 4683854 (1987-08-01), Goulet
patent: 4825836 (1989-05-01), Hirose
patent: 4976226 (1990-12-01), Herman
Dahlgren Mats
Jonsson Nils
Nira Automotive AB
Wolfe Willis R.
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