Fluid handling – Processes – Cleaning – repairing – or assembling
Reexamination Certificate
2000-03-06
2001-08-14
Lee, Kevin (Department: 3754)
Fluid handling
Processes
Cleaning, repairing, or assembling
C137S015180, C251S305000, C251S308000, C251S366000
Reexamination Certificate
active
06273119
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to valves of the type used to switch the flow of exhaust gases automatically from one catalytic converter to another within an exhaust system of a motor vehicle. More particularly, the invention pertains to a method of manufacturing an exhaust control valve so that its valve seats can be machined more easily and at lower cost than the valve seats of the prior art valve. The invention also pertains to an exhaust control valve that that comprises two or more subhousings separately cast and combined together.
BACKGROUND OF THE INVENTION
Federal and state governments have imposed increasingly strict regulations over the years governing the levels of hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxide (NO
x
) pollutants that a motor vehicle may emit to the atmosphere. One approach to reducing the emissions of these pollutants involves the use of a catalytic converter. Placed within the exhaust gas stream between the exhaust manifold of the engine and the muffler, the catalytic converter is one of the several emissions control devices typically found on a motor vehicle.
The catalytic converter is essentially a reaction chamber that contains an oxidation catalyst, typically in the form of one or more monolithic substrates, coated with a high surface area ceramic wash-coat and one or more precious metals such as Platinum, Palladium or Rhodium. When the engine is running, the exhaust gases from the exhaust manifold flow through the converter and pass heat to those composite materials housed within it. Once heated to a suitably high temperature, the composite materials convert a large percentage of the pollutants in the passing exhaust gases to carbon dioxide (CO
2
), water (H
2
O) and other benign substances. Until the converter is brought up to operating temperature, however, its composite materials do not operate as effectively. As is well known, the catalytic converter is particularly inefficient when it is at its coolest, just after the engine is started cold. Consequently, absent other means of reducing such emissions while the engine and converter are warming up, a significant percentage of the pollutants would pass to atmosphere until the catalytic converter is sufficiently heated to operate satisfactorily.
One approach that has been proposed to reduce the emission of HC, CO and NO
x
pollutants while the exhaust system is cold is to use a second catalytic converter, often referred to as a warm-up converter. The warm-up converter would be small in size and located near the engine so that it could warm-up quickly. It would employ composite materials (i.e., a substrate, an oxidation catalyst and catalytic material coating) specially formulated to reach operating temperature quickly, thereby quickly rendering the warm-up converter capable of efficiently converting the pollutants in the exhaust gas. This is significant, as most of the pollutants are produced during the first minute or two after the engine is started. Until the engine and exhaust system have warmed to the point at which the conventional converter is operating more effectively, the exhaust gases during this “warm-up period” would be routed into the warm-up converter to remove the pollutants from the exhaust gases.
Given its proximity to the engine, the warm-up converter will generally not be able to withstand continuous exposure to certain harmful poisons carried by the exhaust gases. In particular, engine oil that may have been burned in the combustion chambers will be carried away by the exhaust gases into the exhaust system. Certain compounds in the oil, such as zinc-dithio-phosphate, will gradually coat the catalyst in the warm-up converter and soon render it ineffective. Prolonged exposure to the exhaust gases will therefore prematurely degrade the composite materials inside the warm-up converter.
A solution to this problem would be to strategically place an exhaust control valve within the exhaust system. Controlled by the engine control module (ECM) or other control component with feedback from a suitable sensor, the exhaust control valve can be automatically opened to allow exhaust gases to flow through the warm-up converter during the warm-up period and closed to prevent such flow afterward. By switching the flow of the exhaust gases away from the warm-up converter after the warm-up period, the exhaust control valve would then protect it from the relatively high temperatures and the harmful compounds carried by the exhaust gases. This tends to keep the warm-up converter free of poisons and highly effective during the warm-up period. After the warm-up period, the conventional converter due to its large size best treats the HC, CO and NO
x
pollutants. The large size of the conventional converter makes it more resistant to such poisoning.
This approach makes best use of both converters. The warm-up converter operates with peak efficiency quickly due to its close proximity to the engine during the critical warm-up period. Thereafter, only the conventional converter treats the exhaust gases. While flowing through the section of the exhaust pipe leading to the conventional converter, the exhaust gases are lowered in temperature somewhat. Soon operating within the desired temperature range, the composite materials in the conventional converter efficiently treat the pollutants in the exhaust gases. Deployed together in this control scheme using the exhaust control valve, the two catalytic converters reduce the HC, CO and NO
x
emissions far better than the conventional converter can alone. This is because they collectively treat the exhaust gases over more of the engine operating time than the conventional converter can by itself.
In such a control scheme, the exhaust control valve must be capable of operating over a wide range of temperatures, for example, from below 0° C. to over 1000° C. In particular, the valve must not stick or bind at any temperature within that range. It must open completely to let the exhaust gases flow through its flow passage. Conversely, it must close with a seal that is sufficient to prevent the exhaust gases from entering the warm-up converter after the warm-up period. Furthermore, the exhaust control valve must not allow exhaust gases to leak outside the exhaust system through its various joints.
A traditional butterfly valve would generally not be suitable for use as an exhaust control valve. The valve body for this type of valve defines a cylindrical inner bore that serves as a flow passage. Through the outer sidewall of the body is defined an opening through which a stem or shaft protrudes perpendicularly into the flow passage. Within the flow passage is placed a circular valve plate. Also referred to as the butterfly, the valve plate typically has an elongated slot formed within it into which the shaft is securely attached. Controlled in a known manner, the shaft can be rotated so that the valve plate, or butterfly, pivots within the flow passage between the opened and closed positions.
The butterfly valve is designed so that when the valve plate is pivoted to the closed position its perimeter contacts the cylindrical inner bore of the valve body. Experience has shown that this design is inadequate for the environment that an exhaust control valve must endure. In particular, the valve plate and body expand and contract, so much so that it is difficult to achieve a good seal over the temperature range to which the valve would be exposed. This design requires the valve body, valve plate and various other parts to be manufactured to meet extremely tight tolerances, thus increasing the cost. Extreme accuracy must be exercised in fitting the valve plate to the inner bore. If the dimensions of these critical parts are not within design tolerances or thermal expansion and contraction are not accounted for, the valve plate in the closed position will fail to adequately seal off the flow passage. In addition, the close proximity of the perimeter of the valve plate to the inner bore of the body tends to cause particulate matter to
Foster Michael Ralph
Smith Kenneth A.
Cichosz Vincent A.
Delphi Technologies Inc.
Lee Kevin
LandOfFree
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