TECHNICAL FIELD
The subject matter described herein, in general, relates to an ignition unit for an internal combustion engine and in particular, relates to a housing structure for the ignition unit.
BACKGROUND
Internal combustion (IC) engines employ ignition units for generating a high voltage spark across a spark generation device, to ignite an air-fuel mixture. One such ignition unit is an electronic ignition unit. The electronic ignition unit typically includes an ignition coil and a control circuit, also referred to as an igniter, housed inside a suitable casing.
To provide a general idea, Fig.la illustrates a conventional ignition unit 100, Fig.lb illustrates a casing 102 for housing the ignition unit 100 of Fig.lb, and Fig.lc illustrates a sectional view of the ignition unit 100 housed inside the casing 102 to form an ignition unit assembly 104.
The ignition unit 100 includes an ignition coil 106 having a primary winding 108 wound around an iron core 110, a secondary winding 112 electromagnetically coupled to the primary winding 108, and a control unit 114. The control unit 114 may include a variety of components such as resistor(s), capacitor(s), transistor(s), integrated circuit (IC) chips, and input and output terminals 116, mounted on a printed wiring board (PWB), for controlling the operations of the ignition unit 100. In operation, one end 118 of primary winding 108 is electrically connected to a primary input terminal 120 of the control unit 114 and another end 122 of the primary winding 108 is electrically connected to a first earth terminal 124 of the control unit 114. Further, an end 128 of the secondary winding 112 is electrically connected to a second earth terminal 126 of the control unit 114. Another end (not shown in the figure) of the secondary winding 112 is

connected to a high tension (HT) terminal 130. The HT terminal 130 is operably connected to a spark generation device such as a spark plug (not shown in the figure) for generating spark. Typically, the control unit 114 controls the current to the primary winding 108, and accordingly the secondary winding 112 generates a high voltage spark across the spark generation device.
Conventionally, the ignition coil 106, along with the control unit 114, is potted together inside the casing 102 using a potting material 132. The potting material 132 performs the function of electrical insulation along with providing protection against environmental factors such as heat, humidity, vibrations etc which may be encountered during the service life of the ignition unit assembly 104. Moreover, due to the constant production of high voltage impulses combined with heating/cooling cycles encountered by the ignition coil 106, over a period of time, the insulation property of the ignition coil 106 deteriorates. The high voltage generated gets discharged internally from the secondary winding 112 to the primary winding 108 or within the secondary winding 112 itself. Since the secondary winding 112 is more prone to the failures, more often than not, the failure of the secondary winding 112 leads to the failure of the whole of the ignition unit assembly 104.
With the recent advent in technology, the durability of electronic components forming the control unit 114 has exceeded over the durability of the ignition coil 106. As a result, the service life of the ignition unit assembly 104 solely depends on the durability of the secondary winding 112 as stated above. Since all the components of the ignition unit assembly 104 are potted together, in case any portion of the ignition coil 106 fails the whole ignition unit assembly 104, including the electronics, needs to be replaced. The replacement of the entire ignition unit assembly 104 leads to a wastage of components that are still in working condition, and hence is not a cost effective option. Further, owing to the requirement of highly efficient insulation across

the secondary winding 112, the entire ignition unit assembly 104 is required to be potted using a vacuum potting technique which further adds to the manufacturing cost of the ignition unit assembly 104.
SUMMARY
The subject matter described herein relates to an ignition unit for an internal combustion (IC) engine. In one embodiment, the ignition unit includes a primary winding and a secondary winding electromagnetically coupled to the primary winding. The primary winding is housed in a first casing to form a first sub-unit and the secondary winding is housed inside a second casing to form a second sub-unit. The second casing includes a longitudinally extending recess for receiving the first sub-unit therein. Further, the first sub-unit is detachably attached to the second sub-unit using a locking mechanism to form the ignition unit.
In another embodiment, the ignition unit may also include a control unit housed inside the first casing.
Owing to the employment of two separate casings, which are detachably attached to each other, the need for replacing the entire ignition unit is eliminated if one of the two sub-units fail to work. In case a component of the ignition unit fails, only the sub-unit having that malfunctioning component can be replaced, thereby lowering the replacement cost of the ignition unit. Further, the components housed inside the first casing may be potted using a relatively low cost potting material or if desired, may not be potted at all, thereby further lowering the manufacturing as well as replacement cost the ignition unit.
These and other features, aspects, and advantages of the present subject matter will become better understood with reference to the following description and appended claims. This

summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
BRIEF DESCRIPTION OF DRAWINGS
The above and other features, aspects, and advantages of the subject matter will become better understood with regard to the following description, appended claims, and accompanying drawings where:
Fig.la illustrates a conventional ignition unit.
Fig.lb illustrates a sectional view of a casing for housing the uncased ignition unit of Fig.la.
Fig.lc illustrates a sectional view of the ignition unit Fig.la housed inside the casing Fig.lb to form an ignition unit assembly.
Fig.2a illustrates a view of a primary winding and a control unit of an exemplary ignition unit, according to an embodiment of the present subject matter.
Fig.2b illustrates a sectional view of a first casing for housing the primary winding and the control unit of Fig.2a, according to an embodiment of the present subject matter.
Fig.2c illustrates a sectional view of a first sub-unit, according to an embodiment of the present subject matter.
Fig.3a illustrates a sectional view of a secondary winding of an exemplary ignition unit, according to an embodiment of the present subject matter.

Fig.3b illustrates a second casing for housing the secondary winding of FigJa, according to an embodiment of the present subject matter.
FigJc illustrates a sectional view of the second sub-unit, according to an embodiment of the present subject matter.
Fig.4a illustrates a sectional view of an assembly of the first sub-unit with the second sub-unit to form an ignition unit, according to an embodiment of the present subject matter.
Fig.4b illustrates a top view of the assembly of the first sub-unit with the second sub-unit of Fig.4a, according to an embodiment of the present subject matter.
DETAILED DESCRIPTION
The subject matter described herein is directed to an ignition unit for generating high voltage sparks across a spark generation device. The ignition unit includes a first sub-unit detachably attached to a second sub-unit. In one embodiment, the first sub-unit includes a primary winding housed inside a first casing. In another embodiment, a control unit may also be housed inside the first casing. Optionally, the first sub-unit may be potted using a first potting material to provide electrical insulation. The second sub-unit includes a secondary winding housed inside a second casing. The second sub-unit can be potted using a second potting material. In one embodiment, the second casing includes a longitudinally extending recess for accommodating the first sub-unit. The two sub-units are physically and electromagnetically coupled to each other to form the ignition unit.
The deployment of two separate sub-units facilitates easy replacement of a non¬functional sub-unit, instead of replacing the entire ignition unit. The ignition unit described

herein may be used for an automotive internal combustion engine for generating spark across a spark generation device such as a spark plug.
Fig.2a illustrates a view of a primary winding 200 and a control unit 202, according to an embodiment of the present subject matter. In one embodiment, the primary winding 200 is electromagnetically coupled to a first core 204 which may be any conventional iron core. Optionally, the first core 204 may be removably inserted in an annular portion of the priming winding 200. The priming winding 200 is electrically connected to the control unit 202. In one embodiment, the control unit 202 may be operably connected to an engine control unit of a vehicle, to control the operations of an ignition unit (not shown in the figure) of the vehicle. In another embodiment, the control unit 202 may function in isolation to control the operations of the ignition unit. The control unit 202 may include resistor(s), capacitor(s), transistor(s), integrated circuit (IC) chips, a primary earth terminal 206, a primary input terminal 208, and multiple input and output ports 210 for receiving and sending signals to a variety of components such as sensors. However, other components may be added or excluded from the control unit 202 without departing from the spirit and scope of the subject matter described.
In one implementation, a first end 212 of the priming winding 200 is electrically connected to the primary earth terminal 206. A second end 214 of the priming winding 200 is electrically connected to the primary input terminal 208 of the control unit 202 for receiving a control signal. Based on the control signal received, the primary winding 200 induces high voltage at a secondary winding (not shown in figure) due to an electromagnetic coupling between the two windings. The electromagnetic coupling has been explained in details later.

Fig.2b illustrates a sectional view of a first casing 216 for housing the priming winding 200 and the control unit 202, according to an embodiment of the present subject matter. The first casing 216 includes a first chamber 218, and a second chamber 220 integrated with the first chamber 218, by means of a connecting region 221, thereby forming a substantially U-shaped casing. The first casing 216 also includes a first element 222 of a locking mechanism. In one implementation, the locking mechanism is used to attach the first casing 216 with a second casing (not shown in the figure). The first element 222 can be disposed on the first chamber 218. In one embodiment, the first element 222 includes a vibration damper 224, such as a lock washer, disposed on the first element 222. The vibration damper 224 provides for close-fitting and firm assemblies and provides protection against loosening resulting from vibrations developed across the secondary winding.
Fig.2c illustrates a sectional view of a first sub-unit 226, according to an embodiment of the present subject matter. The first chamber 218 accommodates the priming winding 200 and the second chamber 220 accommodates the control unit 202 to form the first sub-unit 226. Multiple connecting wires, such as the connecting wires connecting the second end 214 to the primary input terminal 208 and the first end 212 to the primary earth terminal 206 are accommodated in the connecting region 221. In one embodiment, upon accommodating the priming winding 200 and the control unit 202 in the first casing 216, a first potting material 228 may be injected therein. Since, the electrical insulation of the priming winding 200 is less critical than that of the secondary winding, the first potting 228 material can be a low cost potting material with comparatively higher filler content providing reasonable electrical insulation. However, any other potting material known in the art may also be used for potting the first sub-unit 226.

Optionally, the first sub-unit 226 may not be potted at all. Thus, the provision of having an un-potted first sub-unit 226 or using a low cost potting material lowers the manufacturing cost of the first sub-unit 226.
Although Fig.2a, Fig.2b, and Fig.2c are described in detail with respect to an ignition unit having a first casing 216 for accommodating the priming winding 200 and the control unit 202, however many embodiments or variations of the first casing 216 may be made. For example, the first casing 216 may be configured to house only the priming winding 200. and a singular sub-unit thus formed may be operably connected to an external control unit. Further, the U-shape of the first casing 216 is not be construed as a limitation; it would be appreciated by a person skilled in the art that the first casing 216 may have any other appropriate shape.
Fig.3a illustrates a sectional view of an exemplary secondary winding 300, according to an embodiment of the present subject matter. Typically, the secondary winding 300 is composed of a wire with a cross-section less than that of the primary winding 200 and has more number of turns as compared to the priming winding 200. The secondary winding 300 is generally wound over a bobbin 301 that includes an annular portion 302 for receiving the first chamber 218 having the primary winding 200 and the first core 204. Thus, an electromagnetic coupling between the secondary winding 300 and the priming winding 200 is achieved, as in the conventional ignition coils.
Fig.3b illustrates a view of a second casing 304 for housing the secondary winding 300, and Fig.3c illustrates a second sub-unit 306, according to an embodiment of the present subject matter. In one embodiment, the second casing 304 defines a cavity for accommodating the secondary winding 300 to form the second sub-unit 306. A second element 308 to engage with

the first element 222 of the locking mechanism for securing the second casing 304 with the first casing 216, is also provided on the second casing 304.
The second casing 304 also includes a longitudinally extending recess 310 for accommodating the first chamber 218. The longitudinally extending recess 310 may be interchangeably referred to as the recess 310, hereinafter. Optionally, a second core (not shown in the figure) may be removably inserted inside the second casing 304 to form the second sub-unit 306. In said embodiment, in addition to the first chamber 218, the second core may be accommodated in the recess 310. Thus, the second core may be used in conjunction with the first core 204. The second core is accommodated in the recess 310 such that the primary winding 200, may be inserted in a hollow region of the second core. Thus, the second core is placed between the secondary winding 300 and the primary winding 200 to provide an electromagnetic coupling there between.
The second casing 304 also includes an extended portion 312 for accommodating a high tension (HT) terminal 314 that is connected to the secondary winding 300. In one implementation, a first end (not shown in the figure) of the secondary winding 300 is electrically connected to the HT terminal 314 coupled to a spark generation device (not shown in the figure) for generating a high voltage spark across the same. A second end (not shown in the figure) of the secondary winding 300 is electrically connected to a low tension terminal, preferably to a secondary earth terminal (not shown in the figure) of the control unit 202. Optionally, the secondary earth terminal and the primary earth terminal 206 can be a common earth terminal of the control unit 202. Further, the aforementioned electrical connections may be made by soldering the required end of the windings with the corresponding terminals.
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In one implementation, upon assembling the secondary winding 300 with the second casing 304, a second potting material 316, such as epoxy resin, is vacuum injected therein. Thus the secondary winding 300 is electrically insulated, and start and end leads of the secondary winding 300 are firmly fixed by the second potting material 316. Further, depending upon the preferences of a user, a same potting material may be used for potting the first sub-unit 226 and the second sub-unit 306. Additionally, the extended portion 312 accommodating the HT terminal 314 may not be potted.
In different embodiments, the second casing 304 may have a cylindrical, rectangular, square or polygonal cross-section. Also, the second casing 304 and the first casing 216 can be composed of an electrically insulating material and optionally could contain magnetically permeable material. In one implementation, the first casing 216 and the second casing 304 are manufactured using conventional techniques and conventional casing materials.
Fig,4a and Fig,4b illustrate a sectional view and a top view of an assembly of the first sub-unit 226 with the second sub-unit 306 to form an ignition unit 400, according to an embodiment of the present subject matter. The first chamber 218 of the first casing 216 can be inserted in the longitudinally extending recess 310 of the second casing 304, thereby electromagnetically coupling the secondary winding 300 with the priming winding 200. In operation, a control signal, typically a current pulse, is received by the priming winding 200, thereby inducing a high voltage across the secondary winding 300. The high voltage impulse generates spark across the spark generation device.
In one implementation, vibrations developed across the secondary winding 300 due to a sudden change in magnetic flux experienced by the secondary winding 300 are dampened by the
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vibration damper 224. The vibration damper 224 absorbs such vibrations, thereby facilitating a firm and secure fit between the two sub-units 226 and 306. In one embodiment, the two sub-units 226 and 306 are integrated together using a snap-fit mechanism 402, thereby allowing easy engagement and dis-engagement of the first sub-unit 226 with the second sub-unit 306. In said embodiment, the second element 308 may be a tapered cantilever beam, which engages with a mating portion of the first element 222 and compresses the vibration damper 224 to obtain the ignition unit 400.
Although the subject matter has been described in considerable details with respect to the snap-fit locking mechanism 402 for detachably attaching the first sub-unit 226 and the second sub-unit 306; however, it would be appreciated that any other locking mechanism performing the similar function may also be used. For example, the two sub-units 226 and 306 may be fastened using bayonet joints, nuts and bolts, screw threads and like, or any other inter engaging parts which permit steady securing and removal of the two sub-units 226 and 306.
Since the two sub-units 226 and 306 are detachably attached to each other, in case of the failure of a component of the ignition unit 400, only the corresponding sub-unit is required to be replaced. For example, in case of the failure of the secondary winding 300, the electrical connections at the second end of the secondary winding 300 are removed and the second sub-unit 306 is separated from the first sub-unit 226. Thus, a new second sub-unit replaces the non¬functional second sub-unit 306 and is integrated with the first sub-unit 226 thereby forming an ignition unit working for the intended purpose.
The previously described versions of the subject matter and its equivalent thereof have many advantages, including those which are described below. The subject matter described
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herein provides an ignition unit for an internal combustion engine. The ignition unit is provided with replaceable sub-units, thereby lowering the replacement cost of the ignition units. Advantageously, a sub-unit housing a primary winding may not be potted, thereby further lowering the manufacturing and/or replacement cost. Additionally, the proposed ignition unit is reliable and efficient.
While certain features of the claimed subject matter have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the claimed subject matter.

claim:
1. An ignition unit (400) comprising:
a primary winding (200); and
a secondary winding (300) electromagnetically coupled to said primary winding (200);
characterized in that,
said primary winding (200) is housed inside a first casing (216) to form a first sub-unit (226), and said secondary winding (300) is housed inside a second casing (304) to form a second sub-unit (306), wherein said second casing (304) comprises a recess (310) for receiving said first sub-unit (226), and wherein said first sub-unit (226) is detachably attached to said second sub-unit (306).
2. The ignition unit (400) as claimed in claim I, wherein said ignition unit (400) further comprises a control unit (202) operably connected to said primary winding (200). wherein said control unit (202) is housed inside said first casing (216).
3. The ignition unit (400) as claimed in claim 2, wherein said first casing (216) comprises a first chamber (218) for accommodating said primary winding (200), and a second chamber (220) for accommodating said control unit (202).
4. The ignition unit (400) as claimed in claim I. wherein said ignition unit (400) further comprises a first core (204) electromagnetically coupled to said primary winding (200). wherein said first core (204) is housed inside said first casing (216).
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5. The ignition unit (400) as claimed in claim 1, wherein said second sub-unit (306)
comprises a second core, and wherein said second core is accommodated in said recess
(310).
6. The ignition unit (400) as claimed in claim 1, wherein said first sub-unit (226) is potted
using a first potting material (228).
7. The ignition unit (400) as claimed in claim 1, wherein said second sub-unit (306) is
potted using a second potting material (316).
8. The ignition unit (400) as claimed in claim 1, wherein said ignition unit (400) comprises
a vibration damper (224) for dampening vibrations developed across said secondary
winding (300).
9. The ignition unit (400) as claimed in claim 1, wherein said secondary winding (300)
comprises a high tension terminal coupled to a spark generation device.
10. The ignition unit (400) as claimed in claim 1, wherein said first sub-unit (226) is
detachably attached to said second sub-unit (306) by a locking mechanism.
11. An automotive internal combustion engine comprising the ignition unit (400) as claimed
in any of the preceding claims.