The present invention relates to an improvement in sewing machines and more particularly to an improved oil pump for sewing machines.
Proper lubrication of moving parts is an essential feature in industrial sewing machines. For machines presently in use, lubrication may be achieved automatically by means of rotary oil pumps, which serve to continuously circulate a lubricating fluid throughout the machine. The lubricating fluid is typically straight mineral oil having a Saybolt viscosity of 90 to 125 seconds at 100 (F).
Typical of oil pump assemblies presently used for the purposes of sewing machine lubrication is that manufactured by Union Special Corporation, Chicago, Ill., in its Class 36200 machines. In such machines, space for mechanisms and adjustments is at a premium. Therefore, the oil pump assembly in such machines includes two independent gear pumps encased within one housing, both of which are driven by a common spur gear. The spur gear is attached to a gear shaft by means of a gear hub. An oil seal ring and a washer may also be included between the gear hub and the housing wall. The assembly further includes a set of coverplates on either side of the housing. These coverplates may contain a bypass channel for the purpose of metering oil to prevent oil leakage into certain areas of the machine.
A disadvantage inherent in this type oil pump assembly is that it is difficult to machine the housing and the gear hub to achieve a tight fit therebetween, which results in poor pump performance. This may be caused in large part by the difficulty in drilling the shaft hole in the housing square to the housing. If the gear shaft is not square with the housing (i.e., they do not form a right angle with each other), then instead of a tight fit between the spur gear and the inner surface of the housing, these components will meet only at a point. Such a weak seal between the spur gear and housing causes a decrease in pump effectiveness. Wear on the inner surface of the housing caused by the rotation of the components on the interior of the housing further aggravates this problem.
Upon shut-down of the sewing machine, oil may drain from the oil supply tube leading to the pump assembly through a bypass channel located in the coverplate. It is a further disadvantage to the oil pumps presently in use that the oil from the oil supply tube, as well as oil resident within the pump assembly at the time of shut-down, may be drawn out through the bypass channel, because the bypass channel is located in the same horizontal plane as the oil supply tube and the pump assembly. As a result, there is a delay in the supply of oil to the oil pump assembly upon start-up of the machine. This delay results in a build up of friction in the machine which may lead to bearing failure.
It is therefore an object of the present invention to provide an oil pump assembly having tight fitting components so as to prevent a decrease in pump effectiveness.
Another object of the present invention to provide an oil pump assembly of compact size so as to occupy minimal space within a sewing machine.
It is a further object of the present invention to provide an oil pump assembly wherein oil is retained in the oil pump during machine down time so as to minimize the delay in circulating oil to the pump upon starting of the machine.