Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Patent
1998-12-11
2000-01-18
Argenbright, Tony M.
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
F02M 2507, F02D 2108
Patent
active
060149590
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an engine having a management system for controlling the dilution of the mixture supplied to the combustion chambers with recirculated exhaust gases and/or additional air.
BACKGROUND OF THE INVENTION
It is desirable from the points of view of reducing NO.sub.x emissions and improving engine fuel consumption to dilute the mixture supplied to the combustion chambers either by making the mixture lean (air dilution) or by recirculating exhaust gases (EGR dilution). The dilution slows down the burn rate and reduces the gas temperature at the end of combustion and this reduces NO.sub.x formation. Also, the dilution reduces the output power and the engine throttling must be reduced to maintain the same power, which results in reduced pumping losses and improved fuel economy at a given power output.
There is a limit to which the mixture can be diluted with air and/or EGR gases because beyond this limit hydrocarbon emissions become excessive and ultimately the engine becomes unstable and prone to misfire. Engines therefore require careful calibration of the dilution to reduce emissions and improve fuel economy without sacrificing combustion stability.
It is common practice to use both lean burn and EGR dilution in combination and this results in high complexity in the engine calibration because of the number of variables, all of which are interrelated.
In many prior art systems, calibration is achieved by first setting a desired AFR (air to fuel ratio) and subsequently adding EGR dilution to the point where instability commences. This however assumes that the degree of EGR dilution can be controlled rapidly and accurately, which even with the use of closed loop EGR metering systems is not necessarily the case.
The reason why closed loop EGR control is ineffective is that the pressure difference between the intake manifold and the exhaust system varies significantly and rapidly during normal engine operation. At light load, the intake manifold vacuum is high and only a small proportion of EGR dilution is permissible and therefore significant flow restriction is required in the EGR metering system. On the other hand, at higher loads, the manifold vacuum drops while the demand for EGR dilution increases. The net result is that an EGR metering system that is capable of maintaining good accuracy at light load is incapable of meeting the EGR demand at higher loads because of excessive restriction in the EGR metering system.
The control steps in a closed loop control system relying on sensors and intervening actuators also result in slow response so that when the main air flow changes rapidly during transients, the EGR dilution cannot follow at the same rate with the result that the dilution setting is disturbed during the transients.
All these problems make conventional EGR metering systems poor in accuracy and response, expensive and unreliable.
OBJECT OF THE INVENTION
The present invention seeks to provide an engine having a management system that controls the proportion of dilution gases added to the combustible charge of an internal combustion engine and mitigates at least some of the foregoing disadvantages of the prior art.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a spark ignition internal combustion engine comprising: manifold, the main throttle and a point in the exhaust system located downstream of the main restriction to exhaust gas flow, such that the exhaust gas pressure at the latter point is substantially constant during engine operation, and EGR throttle having a similar geometry to the main throttle such that the flow cross sections of the main throttle and the EGR throttle are in a fixed predetermined ratio to one another for all positions of the main throttle.
The pressure upstream of the EGR throttle of the present invention is substantially equal to the pressure upstream of the main throttle and therefore the EGR dilution is always in a fixed proportion to the intake air flow determined by the relative dimensions of the ma
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patent: 4282846 (1981-08-01), Minoura
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Argenbright Tony M.
Castro Arnold
Drouillard Jerome R.
Ford Global Technologies Inc.
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