Patent Application
20120180753
The invention relates to an active thermal shield and diverter of thermal energy.
Heat shields are typically designed to prevent a substance from absorbing excessive thermal energy or heat from an outside source by dissipating, reflecting, or absorbing such heat.
Motor vehicles often use heat shields to manage the thermal conditions because of large amounts of heat given off by internal combustion engines. On most engines, heat shields are used to protect various components and bodywork from heat damage. Additionally, heat shields can provide a performance benefit for the engine by reducing under-hood temperatures in critical locations in order to reduce temperature of the intake air. Automotive heat shields may be formed from a rigid sheet of steel or aluminum, or be formed from flexible aluminum sheeting that is bent manually by the fitter of the shield to conform to the target environment.
In situations where a thermally sensitive component is positioned in close proximity with an extreme heat source, managing thermal energy to prevent detrimental heat absorption by the subject component becomes even more challenging. In such situations, inability to effectively shield the sensitive component may lead to failure of the component and a malfunction of the system in which the component serves a key function. Design and selection of a heat shield for such an application may thus prove critical to the reliability of a subject system and to the satisfaction of the system's user.
A thermal shield-diverter includes a first layer and a second layer. Each of the first and second layers is formed from a material resistant to thermal energy, and each is characterized by a surface having a width and a height. The shield-diverter also includes a third layer formed from a material substantially non-conductive of thermal energy. The third layer is characterized by a third width and a third height, and is disposed between the first layer and the second layer to define at least one passage extending along at least one of the first height and the second height. The at least one passage is configured to divert thermal energy along the respective first and second heights and expel the thermal energy from the shield-diverter when the shield-diverter is exposed to a heat source.
The first width may be substantially equal to the second width and the first height may be substantially equal to the second height. Accordingly, the first and second layers may at least partially overlap the third layer along the first and second heights and may at least partially overlap the third layer along the first and second widths without restricting the passages in the first and second layers. Additionally, the first and second layers may be joined such that the third layer is retained by the first and second layers. The joining of the first and second layers may be accomplished by a crimping process.
The first layer may define a channel extending along the entire first height, and the second layer may define a channel extending along the entire second height. In such a case, the at least one passage may include a plurality of passages such that at least some of the plurality of passages are defined by the channel in the first layer and the channel in the second layer. Additionally, the third layer may define a channel extending along the entire third height such that the at least one passage is defined by the channel in the third layer.
Each of the first layer and the second layer may be formed from either steel or aluminum, while the third layer may be formed from ceramic.
The passage in the first layer may be formed substantially parallel to the passage in the second layer.
An internal combustion engine having an exhaust manifold employing the thermal shield-diverter to divert thermal energy given off by the exhaust manifold away from a sensitive component or area is also disclosed.
The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numbers refer to like components,
As a result of being used to collect post-combustion exhaust gases, the exhaust manifold 12 absorbs significant thermal energy or heat from such gases, such that the surface temperature of the exhaust manifold may exceed 800 degrees C. Throughout operation of the engine 10, the exhaust manifold 12 radiates the absorbed thermal energy to the surrounding environment. The engine 10 also includes a component 14 located proximate to the exhaust manifold 12. The component 14 may include an intricate mechanism and/or various electrical connections, and be unable to withstand direct radiation of thermal energy from the exhaust manifold 12 without a malfunction or outright failure. For example, the component 14 may be a knock sensor such as often used in internal combustion engines for detection of irregular combustion inside the cylinders. As appreciated by those skilled in the art, such a knock sensor is typically incapable of withstanding direct radiation of thermal energy from a proximate heat source such as the exhaust manifold 12.
A thermal shield-diverter 16 is disposed between the exhaust manifold 12 and the component 14. The shield-diverter 16 may be mounted to the exhaust manifold 12, to the component 14, or to some other structure on the engine 10. When the shield-diverter 16 is mounted to the exhaust manifold 12, the shield-diverter 16 may be specifically shaped to cover the exhaust manifold 12 such that the body of the shield-diverter is in the direct path of the heat radiated by the exhaust manifold. The shield-diverter 16 may be mounted to the exhaust manifold 12 to the component 14, or to some other structure on the engine 10 by any appropriate means, such as with bolts or screws (not shown).
Referring to
As shown in
The third layer 38 is characterized by a thickness 39, a third width 40, and a third height 41. The third layer 38 is disposed between the first layer 18 and the second layer 28 such that the channels 26, 36 in the respective first layer and in the second layer form individual and distinct passages 42 and 44. The passages 42 and 44 are configured to divert thermal energy given off by the exhaust manifold 12 along the respective first and second heights 24, 34, and expel the thermal energy from the shield-diverter 16 by a phenomenon called stack effect, as described below. As shown, the passages 42 in the first layer 18 are substantially parallel to the passages 44 in the second layer 28. Furthermore, when the shield-diverter 16 is installed on the exhaust manifold 12, the passages 42, 44 are oriented substantially vertically with respect to the ground. Such orientation of the passages 42, 44 permits the most effective escape of the heated air from these passages.
Stack effect is the movement of air into and out of contained areas in structures such as buildings, chimneys, flue gas stacks, and other containers, and is driven by buoyancy. Such buoyancy generally occurs due to a difference in air density between the contained area and the ambient, typically resulting from differences in temperature and/or moisture. The result of such temperature and/or moisture differences is either a positive or a negative buoyancy force. Ultimately, the greater the thermal difference between the contained area and the ambient, as well as the height of the structure, the greater the buoyancy force, and, therefore, the greater the stack effect.
For the stack effect to be present there has to be a pressure difference “ΔP” between the contained area and the ambient caused by the difference in temperature between those two areas. Such pressure difference is the driving force for the stack effect, and it can be calculated with the equations presented below. The situation in the passages 42 and 44 of
In the international system of units, a.k.a., SI, in the above equation “ΔP” is the available pressure difference in Pascals, “C” is a constant having a value of 0.0342, “a” is atmospheric pressure in Pascals, “h” is height or distance in meters, “To” is absolute outside temperature in Kelvin, and “Ti” is absolute inside temperature in Kelvin. Furthermore, an approximation of the draft or draught flow rate induced by the stack effect can be calculated with the equation presented below. For flue gas stacks or chimneys, where air is on the outside and combustion flue gases are on the inside, the equation below provides an approximation of the draft or draught flow rate induced by the stack effect.
In the SI system of units, in the above equation “Q” is the stack effect draft/draught flow rate in m3/s, “A” is the cross-sectional flow area in m2, “C” is the discharge coefficient (usually taken to be from 0.65 to 0.70), “g” is the gravitational acceleration (defined to be 9.81 m/s2), “h” is the height of the flue gas stack or chimney in meters (m), “Ti” is the average inside temperature in Kelvin, and “To” is the outside air temperature in Kelvin.
By using the above described construction from relatively common materials, the shield-diverter 16 is capable of generating up to a 600 degree C. temperature drop across a distance of 20 mm. Such a significant temperature drop in a relatively short distance is otherwise difficult to achieve without using exotic and expensive materials to cover the exhaust manifold 12. This result is made possible because the shield-diverter 16 does not simply dissipate, reflect, or absorb the thermal energy given off by the exhaust manifold 12, but actually diverts and channels the heat away from the component 14. The overall effect of employing the shield-diverter 16 is to reduce the possibility that damage to the component 14 will occur even when such a component is positioned in close proximity to the exhaust manifold 12.
As may be seen from
In the alternative embodiment, when the third layer 52 is disposed between the first layer 60 and the second layer 62 the channels 56, 58 form individual and distinct passages on each side of the third layer along the height 41. Thus formed, the passages in the final assembly of the shield-diverter 50 become functionally identical to the passages 42, 44 of the shield-diverter 16. As such, similarly to the passages of the shield-diverter 16, the passages of the shield-diverter 50 are configured to divert thermal energy given off by the exhaust manifold 12 along the third height 41, and expel the thermal energy from the shield-diverter 50 by stack effect.
While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.
