Ignition system including spark distribution cassette and ignition coil

A method of making a unitary spark distribution cassette involves molding a cassette and placing electrically conductive lead frames within the cassette during molding. Electrically conductive sleeves for fitting over spark plugs are also provided on the cassette. An ignition system circuit using high voltage diodes in conjunction with an alternating flux ignition coil is placed in the cassette and connected to the lead frames and the sleeves to create a complete electrical circuit. The cassette is then filled with epoxy resin to encase the electrical components to form a unitary package.

TECHNICAL FIELD 
The present invention relates to vehicle ignition systems and more 
particularly relates to a spark distribution cassette for a 
distributorless ignition system which includes an integral ignition coil. 
BACKGROUND ART 
Vehicle ignition systems provide spark to engine cylinders in a controlled 
manner. Conventional vehicle ignition systems for internal combustion 
engines include spark plugs, a high voltage coil and a distributor which 
directs high voltage power through spark plug wires to the spark plugs. 
Recently, distributorless systems which rely upon microprocessor control 
have been introduced to more precisely control engine operation. In such 
systems, the distributor is eliminated and a microprocessor controls 
engine operation based upon data generated as a result of engine 
operation. Systems which utilize a distributor only require a single coil 
for four, six or eight cylinders in standard engine configurations. With a 
distributorless ignition system, one coil is generally used to develop a 
high voltage output for one or two spark plugs. 
When servicing conventional ignition systems, it is necessary to analyze 
each of the components as well as each of the spark plug wires to 
determine which part or parts of the system require repair or replacement. 
This can be quite time consuming and requires skilled mechanics to perform 
the repair. Recently, modular groups of ignition parts have been proposed 
to connect an ignition coil or coils to several spark plugs 
simultaneously. Using a single unit to house the components of an ignition 
system provides advantages when servicing the ignition system. A mass 
produced part can be quickly removed and replaced. The replacement part 
can be fully checked for purposes of quality control resulting in improved 
reliability and customer service. 
Providing a sealed spark distribution cassette including the coil improves 
durability. Housing the components in a single unit also protects the 
individual components from deterioration due to moisture or operation 
under harsh conditions. 
The use of a single coil to provide four high voltage outputs for four 
separate cylinders is disclosed in U.S. Pat. No. 4,392,473 to Tsutsui et 
al. The Tsutsui patent discloses an ignition unit having high voltage 
terminals, high voltage diodes and ignition coils which are assembled 
together and potted in a synthetic resin. Spark plug wires are used to 
connect the output of the coil to the spark plugs. Lead wires are also 
used to connect the high voltage diodes associated with the coil taps to 
the spark plug wire terminals. The assembly of the Tsutsui ignition unit 
is complicated in that many connections to the diodes and coil must be 
soldered or otherwise connected together. The complex installation process 
required by the Tsutsui patent results in a system wherein significant 
costs are incurred for ignition part service. 
A Cassette-type ignition system is disclosed in U.S. Pat. No. 4,706,683 to 
Johansson et al which is designed to be mounted directly over the spark 
plugs of an internal combustion engine. The Johansson patent discloses a 
system wherein circuit boards are imbedded in the unit with epoxy and the 
ignition components of the system are included on the circuit boards. A 
single coil is provided for each engine cylinder. A capacitive discharge 
circuit is used to store charge and provide current to the spark plug. The 
use of circuit boards in the cassette assembly and capacitive discharge 
circuits result in increased cost of the cassette assembly due to 
increased manufacturing and component cost. Many soldered connections are 
required to complete the assembly of the Johansson unit. 
Another example of a modular ignition system is disclosed in U.S. Pat. No. 
4,706,639 to Boyer et al wherein the ignition module is mounted directly 
over the spark plugs of an internal combustion engine. The module 
disclosed in Boyer utilizes one coil for every two cylinders. Wires are 
used to connect the terminals to the ignition coil which necessitates 
soldering connections in the ignition module. 
The present invention is directed to solving the problems confronted by the 
prior art ignition systems and processes for making modular ignition 
system components described above. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a compact, unitary 
ignition system which can be directly mounted over the spark plugs of an 
internal combustion engine and includes a single coil for providing a high 
ovltage spark to four different cylinders of an internal combustion 
engine. Another object of the invention is to provide an ignition system 
wherein no ignition wires are used to connect the coil to the spark plug 
socket, thereby minimizing soldered connections and intricate construction 
operations. 
It is yet another object of the invention to provide a method of making a 
modular ignition system which can be easily automated and performed as a 
highly reliable automated system. 
Accordingly, the present invention relates to an improved spark 
distribution cassette made according to a process wherein the cassette 
housing is molded with a recess large enough to hold the ignition coil and 
secondary distribution circuit components. Lead frames are molded into the 
cassette to provide conductive electrical paths between the ignition coil, 
high voltage diodes and the spark plug receptacles. The high voltage 
diodes are connected to the ignition coil by simply placing them inside 
the cassette where each diode is connected to an electrically conductive 
sleeve adapted to receive a spark plug. The cassette is then filled with a 
synthetic resin to encase the electrical components and form a unitary 
package. By forming a unitary assembly which can be directly mounted over 
spark plugs in an internal combustion engine, the ignition system is 
easily serviced by replacing the entire modular assembly. The elimination 
of high voltage ignition wires improves reliability and simplifies the 
diagnosis of engine operating problems, and also simplifies vehicle 
service procedures. 
Because a single coil may be used to provide a high voltage spark for four 
cylinders, a reduction in the total number of coils needed for an engine 
can be achieved. By reducing the number of coils required it should be 
possible to reduce the cost and weight of the overall ignition system. 
According to another aspect of the invention, lead frames are used instead 
of ignition wires to interconnect the coil to the spark plug receptacles. 
Lead frames also provide the primary electrical connection between the 
vehicle power system and the ignition primary coil. Lead frames are rigid 
conductive members which are easily assembled into the cassette. The lead 
frames include preformed connectors to which the diodes, coil and spark 
plug receptacles are easily assembled. Lead frames also provide a reliable 
electrical connection thereby increase the reliability of the cassette 
during operation.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to FIG. 1, there is illustrated a spark distribution cassette 
assembly, shown generally by reference numeral 10, for use with a 
spark-ignited internal combustion engine, shown generally by reference 
numeral 32. An electronic control unit, not specifically illustrated, 
manages operation of the engine, including control of the spark for the 
combustion process. As shown, the spark distribution assembly 10 includes 
a cassette shell 12 defining a recessed portion 14 or cavity. A plurality 
of sleeves 16 extend from the spark distribution cassette assembly 10. 
Referring now to FIGS. 2 and 3, the internal components of the spark 
distribution cassette assembly 10 will be described. A plurality of high 
voltage lead frames 18 are located within the cassette shell 12. A primary 
coil 20 and a secondary coil 22 are provided to create a high voltage 
output. A magnetic core 23 cooperates with the primary and secondary coils 
to intensify the magnetic fields associated therewith. Diodes 24 are 
placed in the high voltage lead frames 18. 
As best shown in FIG. 1, an epoxy filler 26 fills the recessed portion 14 
of the cassette shell 12, securing the components in the recessed portion 
14 together. In the preferred embodiment, each sleeve 16 includes a socket 
28 which is adapted to be placed over a spark plug 30 of an internal 
combustion engine 32. The spark distribution cassette assembly 10 is 
secured by fasteners 34, such as bolts, to the engine 32. Primary lead 
frames 36 are connected to a receptacle for a low voltage input to the 
spark distribution cassette assembly 10. 
Referring now to FIG. 4a, a circuit diagram illustrating a first flux path 
of the ignition coil is shown wherein an input current I.sub.a is applied 
to the primary coil 20. The flux from the primary coil 20 induces a 
current in the secondary coil 22, setting up a high voltage output by the 
secondary coil 22. As shown, the direction of the input current I.sub.a 
flowing though the primary coil 20 sets up a positively biased input 
resulting in the corresponding positive and negative secondary coil 
voltage outputs. 
With continuing reference to FIG. 4a, the diodes generally referred to 
above as 24 are more specifically shown as 24a, 24b, 24c and 24d to 
explain the alternative flux path circuitry. At the positive output of 
secondary coil 22, diode 24a is electrically connected in the circuit so 
as to conduct the high voltage output to spark plug 30a. Diode 24b blocks 
any output to spark plug 30b. At the negative output of the secondary coil 
22, the diode 24c is electrically connected in the circuit so as to block 
any output to spark plug 30c, whereas diode 24d is electrically connected 
to provide a high voltage output to spark plug 30d. 
Referring now to FIG. 4b, a circuit diagram is shown for an alternative 
flux path wherein an input current I.sub.b is applied to primary coil 20. 
The flux-induced current in the secondary coil 22 sets up a high voltage 
output having a polarity opposite that shown in FIG. 4a. At the negative 
output, diode 24a is electrically connected in the circuit so as to 
prevent energization of spark plug 30a. Spark plug 30b, however, is 
energized by the high voltage spark conducted through diode 24b. At the 
positive side of the secondary coil, diode 24c conducts, allowing a high 
voltage spark to energize spark plug 30c, whereas diode 24d blocks voltage 
from spark plug 30d. 
The method of the present invention will be described in detail with 
reference to FIGS. 1, 2 and 3. The first step in the method is to mold the 
cassette shell 12. The cassette shell is preferably molded to include a 
plurality of preformed electrically conductive lead frames 18 disposed 
within the recessed portion. Primary and secondary coils 20 and 22, 
surrounded by a magnetic core 23, are positioned in the recessed portion 
proximate to each other such that current flowing in the primary coil 
induces a current in the secondary coil. The primary and secondary coils 
are then electrically connected to associated lead frames. The secondary 
lead frames are connected to sleeves 16 which extend from the cassette 
shell 12 into the internal combustion engine. Each sleeve 16 includes a 
socket 28 which receives one end of a spark plug. A plurality of diodes 
are connected to the secondary lead frame members without soldering. The 
lead frame members preferably have lead frames adapted to receive the 
diode leads securely. The cavity is then filled with a potting compound, 
such as an epoxy resin, which seals and secures the component parts within 
the cassette shell. This results in a spark distribution cassette having 
minimal soldering connections, since there are no ignition wires extending 
between the coils and the spark plug sockets. 
It will be readily appreciated by one of ordinary skill in the art that the 
above description of a preferred embodiment of the invention is presented 
by way of illustration and not by way of limitation. The scope of the 
present invention should be interpreted in light of the following claims.