Internal bypass exhaust gas cooler

An exhaust gas cooler assembly (10) with an internally located bypass tube (50), spaced apart from and disposed within a core passage (60), with an exhaust gas inlet manifold (40) directing exhaust gas to a plurality of cooling passages (52, 54, 56, 58) or to the bypass tube (50) by means of control valves (42, 44). Further provided is a detachable valve cartridge (84) with an actuator (16), with all moving components being included within the valve cartridge (84) and actuator (16).

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)

The present invention relates to an exhaust gas cooler component of an exhaust gas recirculation (EGR) system for an internal combustion engine, and more particularly to an exhaust gas cooler with an internal bypass, and optionally with a concentric flow gas intake manifold and valve mechanism.

2. Description of Related Art

EGR systems recirculate at least a portion of the engine exhaust gases into the engine air intake system for the purpose of reducing NOx emissions. Exhaust gas coolers are used to cool a portion of the exhaust gas. Typical prior art exhaust gas coolers are cylindrical shells that define a coolant chamber within the shell. In one prior art embodiment, the engine coolant is caused to flow through the shell, thereby providing a coolant liquid for use in heat exchange. A plurality of small diameter gas cooling passages, such as tubes, transit the length of shell, with each such passage surrounded by the coolant liquid. Thus the exhaust gas is directed through the plurality of small diameter gas cooling passages, and a portion of the heat of the exhaust gas is transferred to the coolant liquid during passage of the exhaust gas through the exhaust gas cooler. The cylindrical shell defining the exhaust gas cooler may have a circular tube plate at each end, sealing the cylindrical tube. The circular tube plates may further have a plurality of holes for receiving, at each end, the plurality of small diameter exhaust gas passages.

As emissions regulations become more stringent, one of the methods of maintaining compliance is to use a bypass exhaust gas cooler which can vary cooling performance depending upon system requirements. For example, at certain times, such as during engine start-up, it is preferable to stop the exhaust gases from being cooled. It is known to utilize an exhaust gas cooler with a separate bypass tube external to the exhaust gas cooler, typically with a valve arrangement, so that exhaust gases can be diverted around the exhaust gas cooler when cooling is not required. This provides a cooling circuit, in which exhaust gas is cooled, and a bypass circuit, in which exhaust gas is not cooled. However, use of a separate bypass tube external to the exhaust gas cooler adds a bulky component to the engine compartment. Particularly with the frequently cramped layout of the engine compartment of a road vehicle, space is at a premium and thus adding a separate bypass tube is not desirable. Additionally, because of the differential rates of expansion and contraction of the exhaust gas cooler and the separate bypass tube during operation, it is necessary to include an expansion means, such as a bellows, to the external bypass tube. This adds to the complexity of construction, adds additional cost, and provides a component that is subject to failure.

It is also known to employ an exhaust gas cooler which diverts all or a portion of the exhaust gas prior to delivery of the exhaust gas to the exhaust gas cooler. For example, one such device employs an exhaust gas cooler which, rather than a cylindrical shell in which gas transits the length of the shell and exits from the end opposite the entrance, has the exhaust gas entrance and exhaust gas exit on the same end, with the exhaust gas reversing direction within the exhaust gas cooler. However, this type of exhaust gas cooler is frequently more bulky than other forms of exhaust gas coolers in which the exhaust gas entrance and exit are on opposite ends. Additionally, this type of exhaust gas cooler requires a redesign of the exhaust gas flow circuit within the engine compartment, is not readily amenable to retrofitting existing engines, and can require significant modifications to engine layouts.

It is advantageous to have an exhaust gas cooler which can be employed such that all exhaust gas is cooled, no exhaust gas is cooled, or only a portion of the exhaust is cooled. Thus in order to provide optimal performance it is advantageous to have an exhaust gas cooler in which not only can the bypass circuit be opened, but also the cooling circuit can be simultaneously physically closed, thereby preventing any exhaust gas cooling in the event that all exhaust gas is diverted to the bypass circuit.

In typical exhaust gas coolers with some form of bypass, the valve assembly for directing exhaust gas to either the cooler circuit or the bypass circuit is an integral part of the exhaust gas cooler or a manifold connected to the exhaust gas cooler. Typically valve components are the only moving parts within the exhaust gas cooler circuit, and include components which are welded or brazed. Because the valve components are movable and actuated by some form of actuator, the components are prone to mechanical failure. However, because of the design of typical exhaust gas coolers, either the entire exhaust gas cooler, or alternatively a manifold or similar component, must be replaced in the event of failure of the valve components. This design adds to costs of construction, since welding or brazing must be performed on a relatively large component, and further increases costs of maintenance, since large components must be replaced in the event of failure of a relatively small sub-component.

BRIEF SUMMARY OF THE INVENTION

The invention provides an exhaust gas cooler assembly including a cooler shell with a first end with a cooler inlet proximate the first end and a second end with a cooler outlet proximate the second end; a plurality of gas cooling passages extending from the first end of the cooler shell to the second end of the cooler shell; a core passage extending from the first end of the cooler shell to the second end of the cooler shell; a bypass tube disposed within and spaced apart from the core passage; an inlet exhaust gas manifold at the first end of the cooler shell and separately in fluidic connection with the plurality of gas cooling passages and the bypass tube; and a valve assembly for selectably controlling an exhaust gas flow to the plurality of gas cooling passages, to the bypass tube, or to a combination thereof. In one embodiment, the gas cooling passages may be parallel to each other and disposed in a concentric array with the core passage centrally disposed within the concentric array of parallel gas cooling passages. The concentric array of parallel gas cooling passages may be a single concentric ring of gas cooling passages or more than one concentric ring of gas cooling passages.

The inlet exhaust gas manifold of the exhaust gas cooler can include a central flow portion in fluidic connection with the bypass tube and a toroidal flow portion in fluidic connection with the plurality of parallel gas cooling passages. Thus there may be provided a first flow conduit in fluidic connection with the central flow portion and a parallel second flow conduit in fluidic connection with the toroidal flow portion. The valve assembly may control flow at the first flow conduit and the second flow conduit. In one embodiment, the valve assembly includes two coaxial butterfly valves, with a first butterfly valve disposed within the first flow conduit and a second butterfly valve disposed within the second flow conduit. The two coaxial butterfly valves may share a common shaft, with the first butterfly valve disposed on the common shaft at a right angle to the second butterfly valve. The valve assembly may be removably engageable from the exhaust gas cooler assembly.

In the exhaust gas cooler assembly, the bypass tube may be connectably engaged to the inlet exhaust gas manifold in a position such that the bypass tube is held spaced apart from the core passage. The bypass tube may also be spaced apart from the core passage by at least three spacers disposed around at least one end of the bypass tube and in contact with the core passage. In another embodiment, the bypass tube is spaced apart from the core passage by at least three spacers disposed around each end of the bypass tube and in contact with the core passage.

The invention further provides an inlet exhaust gas manifold for a generally cylindrical exhaust gas cooler that has a plurality of parallel gas cooling passages arrayed in a ring and a centrally located bypass tube, wherein the manifold includes a first flow conduit in fluidic connection with the bypass tube and a second flow conduit, parallel to the first flow conduit, in fluidic connection with a toroidal conduit, the toroidal conduit being in fluidic connection with the plurality of gas cooling passages. The inlet exhaust gas manifold can further include a valve assembly controlling flow within the first flow conduit and the second flow conduit, and can further include a single axial shaft with a first butterfly valve disposed on the shaft and positioned to control flow within the first flow conduit and a second butterfly valve disposed on the shaft at a right angle to the first butterfly valve and positioned to control flow within the second flow conduit. The valve assembly of the exhaust gas manifold can be actuated by applying a rotational force to the spindle. The manifold can further include actuator for actuating the valve assembly. In one embodiment, the valve assembly is removably engageable from the manifold.

The invention further provides a method of controlling exhaust gas temperature within an exhaust gas recirculation circuit, which method includes the steps of providing a generally cylindrical gas cooler with a plurality of parallel gas cooling passages arrayed in a ring, a centrally located core passage, and a bypass tube disposed within and spaced apart from the core passage; providing an inlet exhaust gas manifold with a first flow conduit in fluidic connection with the bypass tube and a second flow conduit, parallel to the first flow conduit, in fluidic connection with a toroidal conduit, the toroidal conduit being in fluidic connection with the plurality of gas cooling passages; providing an actuator controlling a first valve disposed within the first flow conduit and a second valve disposed within the second flow conduit; and engaging the actuator to control the first valve and the second valve. In the method, the actuator may be engaged in response to a signal from an engine control system, such as in response to at least one input. The inputs can include engine temperature, exhaust gas temperature, engine load or exhaust gas emissions concentrations.

DETAILED DESCRIPTION OF THE INVENTION

With reference toFIG. 1, there is shown an exhaust gas cooler assembly10, including exhaust gas cooler12with an internal bypass. The cooler12has intake manifold and valve assembly14at a first end of cooler12, the intake manifold and valve assembly14further including valve actuator16. Exhaust gas enters the intake manifold and valve assembly14by means of exhaust gas inlet pipe18connected to intake flange20. It is to be understood that exhaust gas inlet pipe18is generally curved, and may include one or more connectors or extenders, and is configured to fit within the engine compartment of a specific engine. Intake flange20is configured to be removably attachable to the exhaust manifold, directly or through one or more intermediate components. The cooler12has a coolant inlet passage24and a coolant outlet passage26, and is connected, by means of pipes, hoses or other conduits, to a circulating coolant source. Typically the coolant source is the engine coolant, such as conventional antifreeze or other coolant, which is circulated by means of a pump associated with the internal combustion engine. However, the coolant source may be any source of fluidic coolant, which may be a liquid or gas, provided only that it is of such a temperature and has suitable heat transfer characteristics that it functions as a coolant. Outlet manifold28is disposed at a second end of cooler12, and is connected to outlet flange22, which in turn is connected to a pipe, hose or other conduit for delivering exhaust gas to the EGR circuit, such as for delivery to an intake manifold of the internal combustion engine (not shown). Cooler12further includes one or more brackets30′,30″,30′″, utilized to fasten and secure exhaust gas cooler assembly10within the engine compartment.

FIG. 2is a midline cross section of a first embodiment of exhaust gas cooler assembly10. Concentric flow intake manifold40includes butterfly valve42, controlling flow to bypass tube50, and butterfly valve44, controlling flow to a plurality of gas cooling passages52,54,56,58. Gas cooling passages52,54,56,58are connected, on the inlet side, to circular tube plate62, and on the outlet side to circular tube plate64. Core passage60is further connected to circular tube plates62,64. The connections between core passage60and circular tube plates62,64, and between gas cooling passages52,54,56,58and circular tube plates62,64, are preferably fluid tight connections, such that pressurized coolant may flow within the spaces between gas cooling passages52,54,56,58without leakage. Disposed within core passage60, and preferably separated therefrom by defined air gap53, is bypass tube50, which on the inlet side is connected to portion41of concentric flow intake manifold40, as shown inFIG. 3. On the exhaust gas inlet side, spacer55spaces bypass tube50away and apart from core passage60. On the exhaust gas outlet side, dimple51spaces bypass tube50away and apart from core passage60. It may be seen that either a spacer may be employed, which may be continuously around bypass tube50, or a series of dimples51may be employed.

In a second embodiment, at each of the inlet and outlet ends of bypass tube50there are disposed three or more equally spaced dimples51, such that bypass tube50is fixed and spaced apart a determined distance from core passage60, thereby defining air gap53. In a preferred embodiment, bypass tube50is fixed with respect to core passage60in all orientations other than axial. In another embodiment, dimples51are disposed on the outlet end of bypass tube50, in contact with core passage60, with bypass tube50held in place on the inlet end solely by means of the interconnection to portion41of concentric flow intake manifold40. Alternatively, dimples or other surface manipulations for location of bypass tube50relative to core passage60may be a feature of core passage60. While dimple51is depicted, which may be formed, for example, by means of a press, it is to be understood that the function may be performed by other forms of spacers, which may be pressed, machined or made by other means. Preferably dimple51or other spacer has as small a contact area with core passage60as is mechanically feasible. It is further preferred to employ no more spacers than is required to space bypass tube50away and apart from core passage60. If only dimples or other spacers are employed, in one preferred embodiment bypass tube50has three radially disposed and equally spaced dimples or spacers at each end of bypass tube50in contact with the inner surface of core passage60.

In order to minimize wear potentially leading to a coolant leak, it is preferred to have dimple51, or other spacer means spacing bypass tube50relative to core passage60, located at a point external to tube plates62,64, as is shown inFIG. 4. This prevents cross contamination of fluids in the event of wear to core passage60by means of abrasion or other failure modes. However, the spacer means may be located anywhere along the length of bypass tube50, or if preferred, core passage60.

The user of spacer means spacing bypass tube50relative to core passage60, with air gap53defined therebetween, permits exhaust gas to pass through cooler12while minimizing loss of temperature; such thermal isolation resulting from the lack of direct contact between the bypass tube50and the coolant, contained by core passage60. The user of spacer means further allows for thermal expansion and contraction without inducing significant stresses into the components.

As shown inFIG. 2, valves42,44may be positioned such as to allow exhaust gas to flow only through bypass tube50as shown by directional arrow A, to flow only through gas cooling passages52,54,56,58as shown by directional arrow B, or a combination thereof, with gases commonly exiting through exhaust manifold28as shown by directional arrow C. In one preferred embodiment, valves42,44are disposed along a common axis, with one butterfly flap disposed at a right angle with respect to the other butterfly flap. By applying rotational energy along the axis, the axis may be rotated such that valve44is closed while valve42is opened, or conversely, such that valve44is open while valve42is closed. It is also possible and contemplated that both valves42and44may be in a partially opened position, such that exhaust gas flows along the paths shown by both directional arrows A and B.

When in partial or full bypass operation mode, such that valve42is partially or fully open, bypass tube50will increase in temperature significantly over the body of cooler12. This gives rise to thermal expansion, which on a conventional cooler design would subject the cooler to stress, particularly axially, where core passage60connects to tube plates62,64. However, by means of dimple51or other spacer means, bypass tube50is rigidly connected at only one end (as shown inFIG. 3), or is not rigidly connected at either end, such as by means of dimples51at each end thereof. This permits axial expansion and contraction of bypass tube50without inducing stress.

FIGS. 5,6and7illustrate aspects of an embodiment of concentric flow intake manifold70, employed with a plurality of a single row of concentric gas cooling passages82, with a centrally located bypass tube78, as shown inFIG. 6. The butterfly valves (not shown) are disposed along common axis72, such that the valves are coaxial, with intake manifold70defining bypass inlet76and cooling passage inlet74, both connectably engaged with tube plate80. Also shown is coolant inlet24, forming a part of cooler12.FIG. 11depicts an end view of tube plate80, showing a plurality of cooling passages82disposed around core passage60, with coolant inlet24and outlet26, together with brackets30′″, also shown.

FIGS. 8,9and10illustrate a further embodiment wherein a detachable valve cartridge84is provided, inserted within a reciprocal bore on concentric flow intake manifold90. Preferably valve cartridge84is cylindrical in shape, fitting within a reciprocal cylindrical bore. Valve cartridge84contains butterfly valves92,94connected to spindle98. Spindle98is rotatably engaged by means of cylindrical hole100, with spindle98transiting through bushing96and connected to crank assembly82, driven in turn by rod80connected to actuator16. Actuator16is fixed relative to valve cartridge84by means of bracket86, it being understood that retaining clips or other fastening means are employed to fasten actuator16and valve cartridge84to bracket86.

As in the previous embodiments, preferably butterfly valve92is disposed along spindle98at a right angle to butterfly valve94, such that in operation when valve92is open valve94is closed, and when valve92is closed valve94is open.

Actuator16is preferably in communication with one or more sensors, and optionally a control system, which sensors control the actuator16. Actuator16is preferably operated by means of a pneumatic vacuum mechanism, but may also be operated by positive pressure, electric or other mechanisms. Actuator16, in response to an appropriate signal, operates the valves, such as butterfly valves92,94, such that if cooling of the exhaust gas is desired, valve94is opened and valve98is closed, such that exhaust gas is directed to flow through the plurality of gas cooling passages, and not through the bypass tube. Alternatively, if cooling of exhaust gas is not desired, then the valves are positioned by actuator16such that exhaust gas is directed to flow through the bypass tube, and not through the plurality of gas cooling passages. Sensors, which may be operably linked to actuator16directly or through one or more intermediate structure, such as a control system, may detect engine temperature, preferably at more than one point, exhaust temperature, intake temperature, load and the like. The control system may further include preset or programmable control circuits, specifying actuator16engagement based on determined parameters and desired emissions compliance.

In one embodiment the invention thus provides for channelling of parallel flows of inlet exhaust gas, controllable by a double coaxial valve, into two concentric flows of gas flow, one directed to the bypass and the other directed to cooling passages. The one piece manifold to direct the flows thus enables use of a simple valve design. In general, flows through the cooler are concentric, and thus would be difficult to valve by conventional means. The outer portion of the cooler flow, which enters the cooler passages, is diverted around the inner bypass in a toroid-like geometry that results in the cooler passage running parallel to the internal bypass tube.

The internal bypass tube may be centrally disposed within a concentric array of gas cooling passages, as shown inFIG. 11. However, other geometric arrangements are possible and contemplated by the invention. For example, it is possible to provide gas cooling passages on one side of a cooler, with the bypass tube located on another side of the cooler. Similarly, while the cooler may conventionally be cylindrical, other shapes are possible, such that the cooler cross section may be oval, square, rectangular or other shapes.

Two valves to control two separate flows or a flow diverter are typically expensive, hard to package in a customer installation and complex. Arranging the flows in a coaxial configuration allows a valve design which is operated by a single shaft axis on which both valves are mounted. Simple butterfly valves may be employed, in that leakage around the valves in the bore is not critical, but alternative valve configurations known in the art could similarly be implemented.

By providing for removable valve cartridge84, problems associated with machine finishing and brazing the valves within manifold70(or any other similar manifold or component) are alleviated. Valve components may become deformed and degraded in a brazing process when the valves form a part of a larger structure, and depending on the configuration, post braze machining may not be feasible. Thus in one embodiment these and related problems are resolved by assembly of all the moving valve components and bushings into a single component, valve cartridge84. It may be seen that post braze assembly of all the moving parts of the valve into a cooler is readily facilitated, and an entire valve component can be fully assembled, finished and tested prior to installation. Valve cartridge84may be cast from stainless steel or another steel alloy, machined, or made by other means. Preferably valve cartridge84is machined in a cylindrical form, which may easily placed into a bore on intake manifold90, or may be located upstream of the manifold, if desired. Once assembled into the cooler or a part thereof, valve cartridge84may be retained by use of a press fit, a clip, or by use of simple fixing means, such as a small screw or rivet. Advantageously valve cartridge84is not subject to the braze process, and thus problems resulting from distortion due to the very high temperatures required for brazing are eliminated. Additionally, the majority of machining is conveniently contained in one component, valve cartridge84. It may further be seen that by this means valve cartridge84may readily be removed, such that the exhaust gas cooler may be easily serviced in the event of valve or actuator failure.

In any of the embodiments, cooler12is conventionally cylindrical in shape, with a circular cross section. However, cooler12may alternatively have an oval, rectangular or other cross section, depending in part on the specific application and the space requirements for the intake manifold and valve assembly. Similarly, while gas cooling passages52,54,56,58and82are shown as cylindrical tubes, with a circular cross section, it is to be appreciated that other geometric configurations of passages or conduits may be employed. For example, the gas cooling passages may be spiral tubes, thereby increasing the surface area of the tube for unit distance length as compared to a cylindrical tube, and thus resulting in greater heat transfer, and further inducing turbulence in the exhaust flow to improve heat transfer by mixing the exhaust gas. The gas cooling passages may further include fins, projections or other modifications intended to increase heat transfer.

The components of the intake manifold and valve assembly are conventionally made from steel, such as a stainless steel or other steel alloy. In one embodiment, a corrosion resistant stainless steel without traces of lead, cadmium, mercury or hexavalent chromium is employed. Depending on the component, the component may be fabricated from sheet material, milled from solid stock, or made by other means known in the art. Components may be assembled by any of a variety of methods; one method employed utilizes tack welding, such as by a tungsten inert gas method, to fix components together, followed by furnace brazing.