Patent Application
20110241521
The present disclosure relates to spark plugs for internal combustion engines and, more particularly, to a spark plug for use in a motor vehicle, co-generation system, or gas feed pump.
This section provides background information related to the present disclosure which is not necessarily prior art. Spark plugs have long been used as igniting means for internal combustion engines of motor vehicles or the like. The spark plug typically includes a center electrode and a ground electrode between which a sparking gap is provided. By applying a high voltage across the center electrode and the ground electrode, a spark discharge takes place in the sparking gap, thereby igniting an air-fuel mixture within the combustion engine.
In recent years and due to an increasing demand for low fuel consumption and high power output, modern motor vehicles generally employ direct fuel-injection type engines each arranged to directly inject fuel into a combustion chamber of the engine. Therefore, the air-fuel mixture supplied to the combustion chamber tends to have an increased concentration of fuel near the spark plug.
In such an arrangement, excess fuel of the air-fuel mixture adheres onto the ground electrode at areas around the sparking gap. Fuel adhered onto the surface of the ground electrode results in some common, problematic issues, such as fuel clamping and fuel bridging. In fuel clamping, fuel flows along the ground electrode surface to a facing surface of the center electrode, congealing therebetween. This problem of fuel of the air-fuel mixture to congeal at the facing surface of the ground electrode increases exponentially over time as engine components wear.
Another common issue is fuel bridging, which occurs when the excess fuel of the air-fuel mixture at the ground electrode surface “bridges” across the sparking gap. Bridging across the sparking gap involves making a connection between the center electrode and the facing surface of the ground electrode causing the spark plug to “short circuit” and misfire. Such issues become especially problematic when starting the engine in an extremely low temperature environment (i.e., fuel is more viscous), which causes fuel clamping and bridging to occur at increased incidence rates.
Attempts to alleviate these problems have included providing spark plugs with center and ground electrodes carrying noble metal chips thereon. The noble metal chips were formed in respective narrowed outer diameters for suppressing the occurrence of fuel bridging (see Japanese Unexamined Patent Application Publication No. 2001-307858). However, even when employing such a spark plug design, the spark plug can still suffer the occurrence of fuel clamping. Further, the addition of noble metal chips in the spark plug design results in increased production time and cost.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. A spark plug for an internal combustion engine includes a housing having a distal end, a proximal end, and an outer periphery extending therebetween. A mounting thread formed on the outer periphery at the proximal end of the housing secures the spark plug to the engine. A center electrode fixedly secured along a central axis of the housing has a first end extending outwardly from the proximal end of the housing. A ground electrode secured to the proximal end of the housing has an electrode tip at a first distance from the center electrode. The electrode tip has a central aperture extending through the ground electrode from an upper surface to a lower surface. A protruding edge circumscribes the aperture and extends a second distance from the upper surface of the electrode tip towards the center electrode.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments will now be described more fully with reference to
Referring now to
The spark plug 12 may include a cylindrical metal housing 22, which may be made of electrically conductive steel (e.g., low carbon steel). The housing 22 withstands the torque of tightening the spark plug 12 into the engine block 16, removes excess heat from the spark plug 12, and disperses the excess heat to the engine block 16. The mounting threads 20 are formed as a lower portion 24 of the housing 22 for attachment into the engine block 16. The housing 22 may contain a porcelain insulator 26 (e.g., an alumina ceramic), which is fixedly and coaxially supported within the housing 22 along a central axis Y. The insulator 26 may include a distal end 28 that protrudes outwardly from an upper portion 30 of the housing 22 and a proximal end 32 that protrudes outwardly from the mounting threads 20. The length of the insulator 26 may be modified to provide an appropriate length for the spark plug 12 per engine design, such that it is more readily accessible for service.
The insulator 26 may also include an axial bore 34 for fixedly retaining a center electrode 36 in an electrically insulated state. A first end 38 of the center electrode 36 may protrude from the proximal end 32 of the insulator 26 such that the center electrode 36 protrudes a predetermined distance from a tip portion 40 of the housing 22.
With reference now to
Operation of the spark plug 12 will now be described with reference to
In excessive fuel conditions, however, such as is found with direct fuel-injection type engines, fuel has a tendency to flow out of the sparking gap 52 into an area away from the reach of the flame kernel form 66 (e.g., onto the middle portion 46 of the ground electrode 42). This excess fuel may gather between the center and ground electrodes 36, 42 resulting in an unfavorable condition, such as fuel bridging or fuel clamping, which may cause misfiring of the spark plug 12. While larger electrode arrangements may produce larger flame kernel forms for consuming this excess fuel, these larger electrode arrangements are more costly, require a higher voltage, and tend to have an increased cooling effect, which may cause ignition to stop short.
The central aperture 56 of the ground electrode 42, however, reduces the necessity for such larger electrode arrangements. The central aperture 56 creates a perforation inside of the ground electrode 42 having the sharp edge 54 around the perimeter for attracting the plasma arc as a grounding point during the ignition sparking process. Such an arrangement allows for a larger electro-magnetic field (EMF) at the sharp edge 54 of the ground electrode 42.
Additionally, the removal of material at the central aperture 56 provides an alternative channel for the flame kernel form 66 to grow. As the flame front of the flame kernel form 66 can now travel vertically, a larger amount of the air/fuel mixture can be ignited in a shorter amount of time, resulting in higher ignitability, improved fuel economy, faster light off times, and better emissions. Further, the central aperture 56 creates a drainage channel for excess fuel, which eliminates the concern of fuel pooling on the ground electrode 42.
A process for forming the ground electrode 42 portion of the present invention will now be described with reference to
Next as shown in
The perforation tool 72 is then pressed through the ground electrode 42 and into a corresponding aperture 80 in the die form 74, thereby removing material from the central aperture 56. As can be understood, the size and shape of the interaction between the perforation tool 72 and the die form 74 may be varied to control the dimensions of the sharp edge 54 at the upper surface 50 of the ground electrode 42.
Finally as shown in
Another embodiment of the present invention will now be described with reference to
Referring now to
The process for forming the ground electrode 142 portion of the second embodiment is substantially similar to that of the ground electrode 42 of the first embodiment and will not be described in detail herein. As can be seen in
The perforation tool 172 is then pressed through the ground electrode 142 and into a corresponding aperture 180 in the die form 174, thereby removing material from the central aperture 156. As can be understood, the size and shape of the interaction between the perforation tool 172 and the die form 174 may be varied to control the dimensions of the sharp spikes 154 at the upper surface 150 of the ground electrode 142.
As the upper surface 50, 150 of the ground electrode 42, 142 has a smaller surface area, fuel is forced to flow out of the sparking gap 52, 152 and into areas away from the ground electrode 42, 142. This prevents fuel from clamping and bridging on the upper surface 50, 150 of the ground electrode 42, 142, which in turn, improves ignitability and startability (i.e sparkability) of the spark plug 12 leading to a longer operating life.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.
