Patent Application
20200088246
The invention relates to an electromagnetic clutch assembly, and more particularly to a thermal fuse of the electromagnetic clutch assembly.
Automobiles commonly include several components that are driven by transmission of a torque from an output shaft of an engine (or other driving mechanism) to the desired vehicle components. In order to prevent inefficient operation of the automobile, it is often desirable to transmit the torque to the components only when the operation thereof is required by the automobile or when the use is desirable to a passenger in the automobile. Such a component may be a compressor forming a component of a heating, ventilating, and air conditioning (HVAC) system of the automobile, as use of the compressor may be dependent on the desire of the user and the conditions of the ambient environment. Accordingly, an electromagnetic clutch assembly may be used to selectively transmit the torque from the automobile engine to the compressor.
However, under certain circumstances, an occurrence of “clutch slip” may occur between the clutch disc 3 and the pulley 2 of the electromagnetic clutch assembly 1. Clutch slip refers to an incidence of relative rotational motion present between the clutch disc 3 and the pulley 2 despite the frictional engagement therebetween. Such a condition may occur when the compressor associated with the electromagnetic clutch assembly 1 seizes, which in turn causes the clutch disc 3 to maintain a rotational position thereof while the pulley 2 continues to rotate via the driving of the associated drive belt. An extended period of clutch slip can lead to damage to an associated pulley bearing, which in turn can lead to a loss of drive belt function in a manner also negatively affecting performance of the engine.
Frictional forces caused by the relative motion between the clutch disc 3 and the pulley 2 during the clutch slip condition lead to the generation of heat. As such, one method of monitoring for an incidence of clutch slip in the electromagnetic clutch assembly 1 includes monitoring a temperature at or adjacent the point of engagement between the clutch disc 3 and the pulley 2. The temperature is monitored in order to determine if the temperature has increased to an extent indicating that a period of clutch slip has occurred.
For example, one solution includes the implementation of a thermal fuse that is configured to activate when a temperature of the thermal fuse is increased to a preselected temperature value. The thermal fuse may include an internally disposed pellet that is configured to melt when exposed to the preselected temperature, wherein the melting of the pellet leads to a reconfiguration of the internal components of the thermal fuse in a manner causing an open circuit condition within the thermal fuse. Upon activation of the thermal fuse, the open circuit condition is communicated to the electromagnetic coil 5 in order to disengage the clutch disc 3 from the pulley 2, thereby ending the relative rotational motion and friction therebetween. The thermal fuse may be disposed at any position adjacent the engagement between the clutch disc 3 and the pulley 2, including on an exposed face of a housing of the electromagnetic coil 5 facing towards the clutch disc 3 as shown in
However, such thermal fuses typically require a clutch slip condition to occur for an extended period of time in order for the thermal fuse to be activated, thereby presenting an opportunity for the pulley bearing to become damaged while the temperature adjacent the thermal fuse has yet to reach the preselected temperature value activating the thermal fuse. For example, such thermal fuses may require about three minutes of continuous clutch slip when the engine of the associated vehicle is idling with an ambient environment at room temperature for the thermal fuse to be thermally activated.
It has been discovered that the bright metallic appearance of the first top plating layer 112 may cause a time delay in activating the thermal fuse 100 following an occurrence of the clutch slip condition. The relatively slow reaction time occurs because the bright metallic finish of the first top plating layer 112 typically includes a relatively low emissivity (generally <0.1 on a 0.0-1.0 scale), which indicates that the top plating layer 112 of the thermal fuse 100 is not well suited for absorbing any incoming thermal (infrared) radiation generated by the frictional forces present between the clutch disc 3 and the pulley 2. As a result, the casing wall 102 is primarily heated only by conductive heat transfer and convective heat transfer, which results in the internal components of the thermal fuse 100 being heated to the desired triggering temperature at a much slower speed than could be realized if the thermal fuse 100 were configured to more readily receive the thermal radiation generated by the clutch slip condition.
It would therefore be desirable to produce a thermally activated fuse having a heat exchange surface with relatively high emissivity in order to quickly and accurately determine that the clutch slip condition has occurred with respect to all possible clutch slip conditions.
Compatible and attuned with the present invention, a thermally activated fuse with a high emissivity surface for increasing heat transfer efficiency through thermal radiation has surprisingly been discovered.
In one embodiment of the invention, a thermal fuse comprises a casing wall configured to transfer heat energy generated exterior to the casing wall to a thermally activated device disposed in an interior of the casing wall. The thermally activated device is configured for activation at a preselected temperature. The casing wall includes a coating layer disposed on an adjacent layer. The coating layer forms an outermost surface of the casing wall and has an emissivity greater than the adjacent layer of the casing wall.
In another embodiment of the invention, an electromagnetic clutch assembly is disclosed. The electromagnetic clutch assembly comprises a pulley, a clutch disc configured to selectively engage the pulley, and a thermal fuse. The thermal fuse includes a casing wall configured to transfer heat generated exterior to the casing wall as a result of relative frictional motion between the pulley and the clutch disc to an interior of the casing wall. The casing wall includes a coating layer disposed on an adjacent layer. The coating layer forms an outermost surface of the casing wall and has an emissivity greater than the adjacent layer of the casing wall.
A method of manufacturing a thermal fuse is also disclosed. The method of comprises the steps of: providing a thermal fuse having a casing wall including an outermost layer, the casing wall configured to transfer heat generated exterior to the casing wall to a thermally activated device disposed in an interior of the casing wall; and forming or depositing a coating layer on the outermost layer of the casing wall, the coating layer having an emissivity greater than the outermost layer of the casing wall.
The above, as well as other objects and advantages of the invention, will become readily apparent to those skilled in the art from reading the following detailed description of a preferred embodiment of the invention when considered in the light of the accompanying drawings:
The following detailed description and appended drawings describe and illustrate various embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner. In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical.
The thermal fuse 10 is configured to be activated when at least a portion of the thermal fuse 10 reaches a preselected temperature indicative of the presence of the clutch slip condition of the associated electromagnetic clutch assembly. As used herein, the thermal fuse 10 being activated refers to a state of the thermal fuse 10 wherein the thermal fuse 10 no longer allows an electrical current to pass therethrough. Prior to the activation, it is assumed that a current is normally capable of passing through the thermal fuse 10 when the associated electrical system is electrically energized.
The thermal fuse 10 may form a component of a circuit used to energize the coil of the electromagnetic clutch assembly. The activation of the thermal fuse 10 may cause a current normally passing through the thermal fuse 10 and energizing the electromagnetic coil to be discontinued. The discontinuing of the current causes the coil of the electromagnetic clutch assembly to also no longer be energized, thereby ceasing the frictional contact present between the clutch disc and the pulley as a gap is formed therebetween following the discontinuing of the electrical current. The thermal fuse 10 may alternatively be referred to as a thermally activated circuit breaker, as desired, without departing from the scope of the present invention.
The thermal fuse 10 may include substantially any internal structure suitable for discontinuing the passage of the current therethrough. As such, the internal structure of the thermal fuse 10 as shown and described with reference to
The thermal fuse 10 as disclosed in
A cylindrical casing wall 30 of the thermal fuse 10 extends longitudinally from a first end 31 to a second end 32 thereof. In the illustrated embodiment, the first end 31 of the casing wall 30 is flared radially inwardly around an end of the second bushing 23 while the second end 32 of the casing wall 30 is flared radially inwardly between an outwardly flared portion of the second lead 14 and a thermal pellet 40 disposed within the casing wall 30. The casing wall 30 forms an outermost portion of the thermal fuse 10 configured for transferring heat generated outside of the casing wall 30 to the components of the thermal fuse 10 disposed inside of the casing wall 30.
The thermal fuse 10 illustrated in
The second bushing 23 includes an axially extending small diameter portion 24 having an outer circumferential surface facing towards an innermost surface of the casing wall 30. A first spring element 4 is disposed between the innermost surface of the casing wall 30 and the outer circumferential surface of the small diameter portion 24. A first end of the first spring element 4 contacts a radially extending surface of the second bushing 23 from which the small diameter portion 24 projects while a second end of the first spring element 4 contacts a slider mechanism 27 slidably disposed within casing wall 30 and formed from an electrically conductive material. The slider mechanism 27 includes an outer circumferential surface in contact with the innermost surface of the casing wall 30.
The thermal fuse 10 further includes a first disk 5, a second spring element 6, and a second disk 7. The first disk 5 is in contact with the slider mechanism 27, the second spring element 6 is disposed between and contacts each of the first disk 5 and the second disk 7, and the second disk 7 contacts the thermal pellet 40. As shown in
As shown in
The coating layer 56 forms an outermost surface of the casing wall 30 exposed to the ambient environment surrounding the thermal fuse 10. The coating layer 56 may be in fluid communication with a supply of air passing over or through the electromagnetic clutch assembly housing the thermal fuse 10. A portion of the coating layer 56 may be in contact with one or more components of the electromagnetic clutch assembly, such as the coil to which the thermal fuse 10 may be mounted as shown with reference to
In the provided example, the casing wall 30 includes each of the base layer 51, an outer under-plating layer 52, an inner under-plating layer 53, an outer top-plating layer 54, an inner top-plating layer 55, and the coating layer 56. The base layer 51 may be formed from a first material, the outer under-plating layer 52 and the inner under-plating layer 53 may be formed from a second material, the outer top-plating layer 54 and the inner top-plating layer 55 may be formed from a third material, and the coating layer 56 may be formed from a fourth material. The outer and inner under-plating layers 52, 53 may be added to the base layer 51 using any known coating deposition method, as desired. The outer and inner top-plating layers 54, 55 may then be added over the outer and inner under-plating layers 52, 53 in a secondary deposition process using any known coating deposition method, as desired. The addition of the layers 52, 53, 54, 55 may preferably be performed prior to the assembly of the remainder of the thermal fuse 10. The coating layer 56 may be added to the casing wall 30 prior to the assembly of the thermal fuse 10 or following the assembly of the thermal fuse 10, as desired. If the coating layer 56 is added after the assembly of the thermal fuse 10, the coating layer 56 may only be added to those portions of the casing wall 30 exposed to the ambient environment, as desired. As such, in contrast to the plating layers 52, 53, 54, 55, the coating layer 56 is only coated on the outermost surface of the casing wall 30.
The selection of each of the materials forming the base layer 51, the outer and inner under-plating layers 52, 53, and the outer and inner top-plating layers 54, 55 may be dependent on the operating conditions of the thermal fuse 10 as well as the method of operation of the thermal fuse 10. The layers 51, 52, 53, 54, 55 may be selected to include a desired degree of thermal conduction for allowing the heat energy generated by the clutch slip condition to be transferred to the interior components of the thermal fuse 10. The under-plating and top-plating layers 52, 53, 54, 55 may be selected to provide a desired degree of corrosion resistance, chemical resistance, strength, durability, or electrical conductivity to the casing wall 30, as desired. As explained hereinabove, at least the innermost layer of the casing wall 30 is formed from an electrically conductive material to facilitate the transfer of the current from the slider mechanism 27 to the casing wall 30.
The first, second, and third materials are all preferably thermally conductive metallic materials. The first material forming the base layer 51 may be an electrically and thermally conductive material such as brass, copper, or alloys thereof, as non-limiting examples. According to one embodiment, the base layer 51 is formed from a sheet of high copper C2300R brass. The second material forming the under-plating layers 52, 53 may be an electrically conductive, thermally conductive, and corrosion resistant material such as copper, nickel, or alloys thereof, as non-limiting examples. The third material forming the top-plating layers 54, 55 may be a thermally and electrically conductive material. The third material may be a highly electrically conductive precious metal such as silver, gold, or platinum. Because the third material forms the innermost surface of the casing wall 30, the highly electrically conductive material may be selected for the top-plating layers 54, 55 to facilitate the transfer of the current through the casing wall 30 for electrically coupling the first lead 12 to the second lead 14. Generally, the materials forming the layers 51, 52, 53, 54, 55 of the casing wall 30 may be selected to form a stable electrical system for transferring a current through the thermal fuse 10.
Although described as being formed from metallic materials, one or more of the layers 51, 52, 53, 54, 55 may alternatively be formed from a non-metallic material having the requisite thermal and/or electrical conductivity for operating the thermal fuse 10 as disclosed herein, such as graphite. In some embodiments, the non-metallic material may be formed as an alloy with an impregnated metallic material, such as an alloy formed from the combination of the graphite and one of bronze or copper, as non-limiting examples.
In one non-limiting example, the base layer 51 is about 0.25 mm thick, each of the under-plating layers 52, 53 is about 1.5-3.0 μm thick, and each of the top-plating layers 54, 55 is about 0.4-2.0 μm. However, each of the disclosed layers 51, 52, 53, 54, 55 may have any desired thickness without necessarily departing from the scope of the present invention. A thickness of the casing wall 30 or each individual layer 51, 52, 53, 54, 55 may be selected to ensure that the casing wall 30 or corresponding layer 51, 52, 53, 54, 55 does not provide an undesired degree of thermal resistance to the heat energy transferred therethrough while also maintaining a desired electrical resistance to the current passing through the casing wall 30.
The coating layer 56 is formed from a material having a greater emissivity than the adjacent layer of the casing wall 30 formed inwardly therefrom, and may include a greater emissivity than any of the other materials forming the casing wall 30. In the illustrated embodiment, the coating layer 56 is disposed adjacent the outer top-plating layer 54, hence the coating layer 56 includes an emissivity greater than that of the outer top-plating layer 54. The coating layer 56 may include an emissivity greater than about 0.5 on a 0.0-1.0 scale. More specifically, the coating layer 56 may include an emissivity of about 0.8 or greater. In some embodiments, the emissivity greater than 0.8 may represent a surface having a substantially black appearance, as desired.
The coating layer 56 may be formed or deposited on the casing wall 30 by one of a variety of different processes. According to a first embodiment, the coating layer 56 may be a chemical conversion coating applied to an outermost layer of the casing wall 30 (the outer top-plating layer 54), and more particularly a black chemical conversion coating having an emissivity of 0.8 or greater. The chemical conversion coating may be formed to be relatively thin (<1 μm thick). The chemical conversion coating may form an inorganic reaction product, an intermetallic material, a metal oxide, a metal sulfide, or an other metal reaction product, as desired. The chemical conversion coating may be a black oxide, a black chromate conversion coating, or a phosphate conversion coating. The chemical conversion coating may be formed during an anodizing process.
The type of reaction product produced is dependent on the chemistry of the material or materials used to form the chemical bath used in the conversion process. For the purposes of the present invention, it is understood that any form of chemical conversion process suitable for increasing the emissivity of the exposed surface of the casing wall 30 while maintaining suitable heat exchange and corrosion resistant properties may be utilized without necessarily departing from the scope of the present invention.
According to a second embodiment of the invention, the coating layer 56 may be formed by a vapor deposition method. The vapor deposition method may be a chemical vapor deposition (CVD) method or a physical vapor deposition (PVD) method. The resulting coating layer 56 may be relatively thin (<1 μm thick) and may include an emissivity of 0.8 or greater. The material deposited may be a ceramic coating or a carbon coating. If a ceramic coating is used, the ceramic may be a compound including a combination of a metal and at least one metalloid or at least one non-metal. The metalloid or non-metal may be one of boron, carbon, nitrogen, oxygen, fluorine, silicon, phosphorous, sulfur, chlorine, arsenic, selenium, bromine, tellurium, iodine, lanthanum, cerium, praseodymium, astatine, or combinations thereof.
According to a third embodiment of the invention, the coating layer 56 is formed from an electrically conductive carbon paint or an electrically conductive enamel coating. The carbon paint or the enamel coating may be provided with an emissivity of 0.8 or greater and may be formed to be about 5 μm or greater in thickness.
Accordingly to a fourth embodiment of the invention, the coating layer 56 may be formed from an electrically non-conductive black organic paint coating. The black organic paint coating may be provided with an emissivity of 0.8 of greater and may be formed to be about 15 μm or greater in thickness.
The increased emissivity of the coating layer 56 in comparison to the relatively low emissivity outer top-plating layer 54 increases a heat transfer efficiency of the thermal fuse 10 when encountering thermal radiation generated exterior to the casing wall 30 of the thermal fuse 10, thereby reducing the time required for the thermal fuse 10 to determine that the clutch slip condition has occurred. The thermal fuse 100 can accordingly react to the clutch slip condition in a relatively short time period regardless of the ambient air temperature or engine condition.
During normal operation of the associated electromagnetic clutch assembly, the current used to power the associated electromagnetic coil normally passes through the thermal fuse 10 when the thermal fuse 10 is in the configuration shown in
The aforementioned repositioning includes the slider mechanism 27 spaced from the end of the first lead 12. The new position of the slider mechanism 27 is determined by a configuration of each of the first and second springs 4, 6 wherein the corresponding spring forces acting on the slider mechanism 27 by the first and second springs 4, 6 are equalized. The spacing of the slider mechanism 27 from the first lead 12 causes the current passing through the first lead 12 to no longer pass through the slider mechanism 27, the casing wall 30, and the second lead 14, thereby discontinuing the passage of the current from the associated power source to the electromagnetic coil of the electromagnetic clutch assembly. The activation of the thermal fuse 10 accordingly leads to the clutch disc no longer being in frictional engagement with the rotating pulley, thereby ceasing the clutch slip condition.
As explained hereinabove, it should be apparent to one skilled in the art that the internal structure of the thermal fuse 10 may be reconfigured to a plurality of different suitable configurations for ceasing the passage of the current through the thermal fuse 10 without necessarily departing from the scope of the present invention. For example, any suitable assembly of internal components of the thermal fuse 10 wherein the melting of a thermal pellet similar to that shown and described in
The thermal fuse 10 may accordingly be described as including a casing wall configured for transferring the heat generated as a result of the clutch slip condition therethrough and to a thermally activated device disposed within the casing wall, wherein the thermally activated device is configured for activation as a preselected temperature indicative of the occurrence of the clutch slip condition. The inclusion of the coating layer on what would otherwise form the outermost surface of the casing wall aids reducing the amount of time required for activating the thermally activated device disposed within the casing wall.
From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.
This patent application claims priority to U.S. Provisional Patent Application No. 62/731,352 filed on Sep. 14, 2018, the entire disclosure of which is hereby incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62731352 | Sep 2018 | US |
