Ignition coil with microencapsulated magnets

Details Ignition coil with microencapsulated magnets Ignition coil with microencapsulated magnets

2000-03-03

2001-02-13

Donovan, Lincoln (Department: 2832)

Inductor devices

Combined

With connector

C336S110000

Reexamination Certificate

active

06188304

ABSTRACT:

TECHNICAL FIELD
This invention relates to an ignition coil for a spark ignition engine, and more particularly to an ignition coil having microencapsulated magnets to reduce eddy current losses.
BACKGROUND OF THE INVENTION
It is well known in the art of ignition systems for automotive vehicles to have an ignition coil that produces magnetic energy upon discharge to create a high voltage spark to initiate combustion in an engine cylinder. Permanents magnets may be used to bias the core in the ignition coil to permit an increase in the stored magnetic energy in a magnetic circuit of the ignition coil.
Typically, an ignition coil includes primary and secondary windings each wound around a spool and disposed about a cylindrical magnetic core with the primary winding surrounding the secondary winding. Cylinder shaped permanent magnets are disposed at the ends of the magnetic core. To make this type of ignition coil compact, the magnetic core is made smaller than in other types of ignition coils. However, one drawback with this type of ignition coil is that, due to the levels of bias required with the small cores, the magnets have to have a very high energy product. This requirement limits the useable material for the magnets to materials like sintered neodymium-iron-boron (NdFeB) and samarium-cobalt (SmCo). The sintered magnets have a very low resisitivity, 2×10
−4
ohm-cm, which yields high eddy current losses in the magnets. Usually, the diameter of the magnets is the same as the diameter of the magnetic core and they are typically 4 to 5 mm long. This creates a large eddy current path around the diameter of the magnets, resulting in an eddy current loss that is proportional to the diameter squared. In some coil designs, 15 to 20% of the energy lost is due to the eddy current losses in the magnets. There is a need to reduce the magnet eddy current losses to improve the efficiency of the ignition coil.
SUMMARY OF THE INVENTION
The present invention provides an ignition coil for a spark ignition engine having microencapsulated permanent magnets to reduce eddy current losses. The coil includes a magnetic core having opposite first and second ends. The magnetic core is a cylindrical member preferably having a circular cross section. At least one magnet is disposed at one of the ends of the magnetic core. Magnets are preferably disposed at both ends of the core. A primary winding is wound about the magnetic core between the first and second ends. A secondary winding assembly is disposed about the primary winding and the core. The assembly includes a spool and secondary winding wound thereon. The secondary winding is inductively coupled to the primary winding. An outer case is disposed about said magnetic core, magnets and the primary and secondary windings.
The present invention provides an efficient ignition coil by reducing the eddy current losses of the permanent magnets. The eddy current losses are reduced by making the permanent magnets from microencapsulated magnetic material. The magnets are made of a powder of rare earth, high energy materials such as neodymium and samarium dispersed within a binder, such as a plastic or epoxy. In one embodiment the powder is made from NdFeB and is compacted to yield a high density. The microencapsulated magnets provide a magnetic core biasing that is less than the biasing obtained with a sintered NdFeB or SmCo magnet. However, the decrease in energy is made up by the fact that the eddy current losses are negligible due to the increased resisitivity of the material. The resisitivity of the material is from 2×10
−3
to 1×10
−1
ohm-cm, resulting in kilovolt performance that is approximately identical to the other type of ignition coil. The lower core biasing can also be offset by the use of a larger magnetic core.
The present invention also provides an ignition coil with increased voltage at a given charge time and primary current over an ignition coil having sintered NdFeB and SmCo magnets. When using microencapsulated magnets, less energy has to be stored for the same voltage, which allows the charge time and primary current to be limited, resulting in an ignition coil that offers superior performance.


REFERENCES:
patent: 4981635 (1991-01-01), Yamashita et al.
patent: 5190684 (1993-03-01), Yamashita et al.
patent: 5335642 (1994-08-01), Hancock et al.
patent: 6025770 (2000-02-01), Okamoto et al.
patent: 6039014 (2000-03-01), Hoppie
patent: 10-223464 (1998-08-01), None

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