Measuring and testing – Simulating operating condition – Marine
Reexamination Certificate
2003-02-28
2004-11-02
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Simulating operating condition
Marine
Reexamination Certificate
active
06810725
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to exhaust gas recirculation (EGR) systems. In particular, the present invention is directed to exhaust gas recirculation measurement devices for EGR systems that allow measurement of exhaust gas flow, even when the exhaust gas is flowing in a reverse direction.
2. Description of Related Art
The standards for vehicle emissions and other applications utilizing internal combustion engines have continued to increase to minimize environmental impact of fossil fuels. In particular, governmental regulations continue to require more and more fuel efficient vehicles and internal combustion engines with reduced emissions. Various emission components such as hydrocarbons (HC), nitrous oxides (NOx), particulates and other emission components have been significantly reduced recently by internal combustion engine manufacturers in view of these regulations, and the benefits to the environment. Many different methods have been utilized by manufacturers of internal combustion engines to reduce emissions including the use of catalytic converters, particulate traps, exhaust gas recirculation (herein after “EGR”) systems, as well as other devices and techniques.
EGR systems typically operate by diverting a portion of the exhaust gases emitted by the internal combustion engine back to the intake airflow of die engine. The recirculated exhaust gas mixes with the intake air and is used in the combustion of additional fuel. Such recirculation of at least a portion of exhaust gases generated by the internal combustion engines reduces emissions of the engines, and has been used in the automotive industry for many years. To ensure proper operation of the internal combustion engine, the amount of exhaust gas that is recirculated by the EGR system must be controlled based on the operating conditions and parameters of the engine. Thus, many EGR systems include a valve that regulates the amount of exhaust gas that is recirculated to the intake of the engine, the valve being controllable based on the operating conditions and parameters.
In the above regard, various EGR systems have been proposed in the art. For example, Japanese Patent 3-290051 to Makoto discloses an EGR system where a portion of the engine exhaust gas is introduced into a suction pipe and a single pitot tube is installed at the exhaust part of an EGR passage. U.S. Pat. No. 6,230,697 to Itoyama et al. discloses an EGR control system which includes an air flow rate detection means for detecting a flow rate of intake air drawn into an internal combustion engine to output an air flow rate indicative signal. However, Itoyama et al. does not disclose a particular device for accomplishing the desired air flow rate detection.
Moreover, whereas various other devices for measuring airflow are known in the art, such devices are not applied to EGR systems of internal combustion engines and have not been shown to be effective in such applications where the gas being measured is exhaust gases of internal combustion engines having emission components of combustion such as particulates.
For example, U.S. Pat. No. 4,478,075 to Oyama et al. discloses an air flow meter where a protective plate associated with the upstream inlet is provided on the upstream side of a by-pass passage to prevent dust from entering the by-pass passage. The flow meter includes a venturi structure connected to a passage that is connected with the main passage via rectangular bore. Oyama et al. also discloses that the ratio of a flow rate of the air flowing in the by-pass passage to that of the air flowing in the main passage is set in advance to a predetermined level. The Oyama et al. reference further discusses the issue of reverse flow in an engine air handling system as it relates to intake air, but does not discuss an EGR measurement device that is used for an EGR system.
U.S. Pat. No. 3,910,113 to Brown discloses a pipe insert having a pressure sensing form including high pressure and low pressure taps on the high pressure and low pressure sides of the form. The Brown reference further discusses the issue of reversed flow within the pipe. However, the Brown reference does not disclose or otherwise suggest use of the pipe insert with an EGR system. U.S. Pat. No. 4,463,601 to Rask discloses a mass airflow measurement apparatus which addresses the issue of reverse flow. The apparatus of Rask includes center body which divides the airflow of the engine into two concentric branches which have different flow splits in forward and reverse directions where the reverse flow in one of the branches is greater than in the forward flow. The Rask reference, however, does not disclose or suggest the use of the mass airflow measurement apparatus in an EGR system.
U.S. Pat. No. 5,088,332 to Merilainen et al. discloses a gas flow restricting and directing device that measures flow in medical respirators and also addresses the issue of reverse flow. The gas flow restricting and directing device of Merilainen et al. includes apertures around which vanes or baffles are provided. However, as noted, this reference relates to medical respirators and does not disclose or otherwise suggest use of the gas flow restricting and directing device that measures flow in an EGR system.
As evident from the discussion provided below, there exists an unfulfilled need for an EGR measurement device that will allow precise measurement of the exhaust gas recirculated. There also exists an unfulfilled need for such an EGR measurement device that will allow measurement of exhaust gas recirculated when the exhaust gas is flowing in the reverse direction. There further exists an unfulfilled need for such an EGR measurement device that is cost effective to manufacture.
SUMMARY OF THE INVENTION
In order for the EGR system to precisely regulate the amount of exhaust gas that is recirculated into the intake of the internal combustion engine, accurate measurement of the EGR flow is required. It has been found that EGR flow is highly pulsitile, i.e. occurs in pulses, due to the exhaust valve events. The portion of the exhaust gas being recirculated generally flows from the exhaust of the internal combustion engine to the intake of the internal combustion engine. However, there are short periods of time where the flow of the exhaust gas in the EGR system reverses in direction so that the exhaust gas being recirculated flows from the intake side to the exhaust side of the internal combustion engine as the pressure in the exhaust manifold bottoms out.
The current method of quantifying EGR flow is to measure the pressure differential across an EGR measurement device in the EGR system that produces a total-to-static pressure drop. The Bernoulli equation is then used with the measured pressure differential to calculate the flow rate of the exhaust gas being recirculated to the intake of the internal combustion engine. As noted above, because the flow direction actually reverses for short time periods, it has been found to be desirable to provide a measurement device that allows a total-to-static pressure to be produced regardless of the direction of EGR gas flow. The prior art devices described above which are applicable to EGR systems do not have this capability of measuring exhaust gas recirculation flow when the exhaust gas is flowing in a reverse direction, and do not even recognize this issue of reverse flow in EGR systems.
FIG. 1
shows graph
1
with the desired pressure response as line
2
which may be attained by implementing the measurement device using an orifice in both the forward flow direction and the reverse flow direction. As shown, the x-axis of the graph
1
indicates the mass flow in pound of mass per minute (lbm/min) while the y-axis of the graph
1
indicates the delta pressure, i.e. the pressure differential, in pounds per square inch (psid). As shown, for the same mass flow, the pressure differential (delta-P) is the same magnitude in the reverse direction as it is in the forward direction except the changes in sign. The
Braun Jeffrey J.
Henderson Gregory H.
Marthaler Michael J.
McKinley Thomas L.
Pan Guangping
Brackett, Jr. Tim L.
Cummins Inc.
Lefkowitz Edward
Nixon & Peabody LLP
Schelkopf J. Bruce
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