This invention relates to an improvement in a rotor arm of a distributor of a spark-fired internal combustion (IC) engine which is intended to increase the horsepower of the engine and at the same time to economise on the fuel consumption of the engine.
A distributor rotor functions to distribute electrical current to spark plugs of an IC engine causing them to ignite fuel vapour in the cylinders of the engine and put the engine in motion. The rotor is usually made of a plastics core and a conducting plate (usually a brass plate) secured thereto. Generally, the thickness of the conducting plate is less than 1.7 millimetres and its design has changed little over many years.
The rotor arm rotates within a ring of stationary contacts (usually one for each cylinder of the engine) whereby current at high voltage fed to the axis of the rotor arm can spark across between the outer tip of the conducting plate and each stationary contact in turn as the rotor arm turns during operation of the engine.
The German language textbook "Werkstoffkunde für die Electrotechnik und Elektronik" (VEB Technik Berlin, 1986) discloses that either brass or a number of different bronze alloys (such as Cu-Sn, Cu-Ag, Cu-Al, Cu-Be, Cu-Mn and Cu-Ni) may in general be used as the material for electrical contacts, but there is no specific suggestion that these materials are suited for distributor rotor arms. The amount of copper in the bronze alloys is stated to be over 60%.
With the widespread use of spark-fired IC engines in motor vehicles, any improvement in power output and/or fuel economy of the engines is widely sought. This invention promises improved performance of a spark-fired IC engine by means of a simple but unobvious modification of the distributor rotor, a cheap, readily-changeable spare part of such engines.
The invention provides a rotor arm distributor for a spark-fired internal combustion engine, the rotor arm comprising a conducting plate on a core support, characterised in that the conducting plate is provided with a tin layer on the tip portion thereof.
The conducting plate may be of brass, and the layer of tin may have a thickness of between 1mm and 2mm, preferably about 1.5mm. Preferably, an increased edge area of the tip of the conducting plate of the rotor arm is provided, such that the area of the conducting plate available for current transmission when the rotor arm revolves within the ring of stationary metal contacts in the distributor cap is increased, thus allowing a stronger electrical current to be conducted to the spark plugs.
A rotor arm improved in accordance with this invention has been found to produce a more powerful spark at the plug and thus better combustion and cleaner engine running with a consequent increase in engine horsepower, between 5% to 10% improvement in fuel combustion and reduced air pollution from the engine exhaust gases.
The invention will now be further described, by way of example, with reference to the accompanying drawing, in which:-
The rotor arm 10 shown in Figure 1 consists of an electrically-insulating core support 11 (e.g. of ebonite) carrying an electrically-conducting radial plate 12 (e.g. of brass) having a tip 13. High voltage for firing each spark plug is led to the radially inner end of the plate 12 and passes through the plate to spark across from the tip 13 to a stationary contact (not shown) as each spark plug is energised in turn as the rotor arm 10 rotates about the axis 14. The plate 12 would typically be of 1.5 millimetres thickness at the tip.
The rotor arm 10 shown in Figure 2 differs from that shown in Figure 1 by the provision of an extension 15 to the tip 13, and by the provision of a tin layer on the tip portion. In the illustrated embodiment, the extension 15 is of tin or a tin/brass alloy which is at least as thick as the plate 12 at the tip 13 and has a radial extension of between 1 and 2 millimetres and has an extension in the circumferential direction of travel of the arm which substantially matches that of the tip 13. The ratio of tin to brass in the alloy can be about 50:50%.
In a modification, the extension 15 is of brass but has a thickness in the axial direction of the core support 11 of between 1.75 millimetres and at least 3.0 millimetres.