Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-04-17
2003-03-04
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06800R
Reexamination Certificate
active
06528911
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to automotive-type rectifier assemblies used to convert polyphase alternating current to direct current using silicon semiconductor diodes. More particularly, the invention deals with the high power and under-hood temperatures required by modem day automobiles and the problems associated with overheated and stressed semiconductors. Further, the invention relates to the complex manufacturing and operational problems associated with the sensitivity of semiconductors to the heat, stress and mechanical forces, as well as a method of manufacturing semiconductors, thus eliminating these problems.
2. Description of the Related Art
Much work has been done in the past to decrease manufacturing costs, air pollution and weight, thus decreasing the alternator's size. Paradoxically, the electrical energy requirements increased. Compact alternators operating under these conditions cannot dissipate heat out of the rectifier bridge fast enough to prevent semiconductor failures. This is particularly true during the summer months when the ambient temperatures are quite high, providing minimal heat transfer and a higher alternator failure rate.
The present invention addresses these problems, especially the replacement expenses for the remanufacturing industry, the general public, and also the wasted energy.
The present invention is further concerned with state of the art manufacturing, because of the chip's extreme sensitivity to the thermal and mechanical stresses associated with it. The invention described herein avoids the stresses by never exceeding the semiconductor's technical and handling specifications. The new and novel invention decreases the horrendous alternator failure and return rate caused by the semiconductors. This is a general nuisance for the public, costing millions of dollars, for towing, repairs and replacement alternators, wasting energy and generating unnecessary air pollution.
The prior art teaches that polyphase alternating current can be converted to direct current by conducting it through six or more semiconductors pressed into prepunched holes in the rectifier heat sinks used in the automobiles' alternators, as illustrated by U.S. Pat. Nos. 5,043,614 and 5,712,517, which are incorporated by reference herein.
The above type inventions are complex to manufacture because the semiconductor chip's extreme sensitivity to the heat, stress and mechanical forces applied during the manufacturing of rectifier bridges causes production failures and causes premature catastrophic failures during the vehicle operation.
Historical data collected from returned alternators under warranty indicate their semiconductors have a very high mortality rate. Historically, 74% fail within the first month's operation, 15% during the next 2 months, 4% after
3
months and 7% during the next 4 months. This failure rate can be directly correlated to manufacturing damage.
This is especially so because silicon semiconductor chips are extremely fragile, being only 0.180×0.180×0.007 inches thick (the thickness of three human hairs), making them so sensitive to the pressure, stress and heat, which are all required to press them into the state of art rectifier bridges.
When chips this thin are soldered inside the bottom of a thick copper cylinder and then filled with an epoxy, a solid mass is formed. Being solid, the chip has no clearance for thermal or stress relief, all transmitted into them during soldering, installation and the alternator operation. Therefore, if a prestressed, overheated chip does not fail during the manufacturing and testing, if damaged, it will likely fail in the alternator, exposed to the constant heating, cooling and load changes. Thus, the chips have a high morality rate.
Most press-fit rectifier bridges incorporate two heat sinks, one usually being a positive aluminum heat sink, the other being the negative die-case aluminum rear alternator housing. They are separated from each other by a heat conductive, electrical insulator gasket or a ceramic coating on the housing, which is a very expensive process. Both of the heat sinks have prepunched or machined holes for at least three press-fit semiconductors. The cathodes of the first three are pressed into the positive heat sink, and the anodes of the other three are pressed into the negative heat sink. At least three stator terminals, stamped out of copper, are usually encapsulated into a plastic assembly. Each has two locating holes to affix a positive set and a negative set of semiconductor leads in series, along with a slot, which connects a set of stator field leads between them.
The first set of stator terminals connects the anode lead from the first positive semiconductor to the cathode of the first negative semiconductor, thereby forming a set of series connected semiconductors between the two heat sinks. The leads from the alternator's polyphase field winding is affixed into the slot, which connects it between the series diodes, as described above. The next two sets of semiconductors are similarly connected to the second and third sets field windings, completing the polyphase field circuits. A lead for the voltage regulator is also affixed between the third set of semiconductors. A stud is affixed to the positive heat sink to complete the B+ circuit to the positive post of the battery. Likewise, the negative heat sink completes the charging system's circuit to the negative post when the alternator is installed.
Prior to assembling the rectifier bridge, a thin coating of thermally conductive grease is applied onto the surfaces of the heat sinks in an attempt to increase the heat transfer out of the semiconductors affixed to the positive heat sinks, through the insulator gasket and into the aluminum die-cast rear housing, into the cooling air flow. However, the semiconductor chips are affixed deep into thick copper cylinders, surrounded by an epoxy filler, thus delaying the heat transfer out of them and causing even more chip failures.
The automotive industry being very competitive, continually requires cost efficiency and less failures.
SUMMARY OF THE INVENTION
State of the art rectifier bridges using pressed-in semiconductors are a continuous nuisance and problem for the general public, requiring expensive service calls, towing and repairs. It is the object of the present invention to eliminate this costly nuisance by eliminating these failure problems, further advancing the state of the art by its unique design, creating a method of manufacturing the bridge rectifier without stressing or damaging the sensitive semiconductor chips inside the diodes. It also instantly dissipates their heat out directly into the outside cooling air, being affixed directly onto copper assemblies and stator terminals, which are in direct contact with the cooling air flow. The thermal transfer (compound) gasket also transfers the heat directly into the housing and to the outside cooling air quicker.
The invention is so unique that thousands of dollars can be saved by using it to remanufacture existing rectifier bridges discussed above. This is accomplished by machining off the upper section of the press-fit copper cylinders (removing the plastic and chip section), which is then pressed out of the sinks. The blank copper slugs are placed into hydraulic press fixtures and pressed into solid copper cavity nest assemblies, which will then nest the pan and/or button type semiconductors.
The newly formed copper assemblies are then pressed back into the existing heat sinks, without chips. The reused copper not only decreases the manufacturing cost but also saves our precious earth elements and the energy required to manufacture new ones. The present invention is especially unique because it decreases the horrendous failure problems associated with the present state of the art rectifier bridges, which is the primary cause of alternator failures. However, the known bridges are remanufactured, only to fail again, b
Electro-Dyn Electronics Corporation
Perez Guillermo
Ramirez Nestor
LandOfFree
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