Abstract: An electric actuator that is structured simply, low in costs and high in both energy efficiency and operation accuracy and is capable of realizing frequent activation and stop is provided. In a return stroke in which a linear actuator is in low load operation state, an energy generated by an electric motor and a kinetic energy generated by movable portions when they stop are absorbed and accumulated by a coil spring. By this constitution, it becomes possible to cause the movable portions of the linear actuator to quickly stop while eliminating the necessity of giving a braking force by an electric or mechanical brake or the like and of providing a configuration designed for giving a braking force in a reliable manner such as one provided as a measure against heat generation. On the other hand, in an actuation stroke, the energy accumulated in the spring is released as operation energy of the movable portions when the spring extends and a driving force required of the electric motor is reduced.

Abstract: A pumping system for oil production comprises a hydraulic unit set on the ground and adapted to send out a pressure oil, and a pump unit set in an oil well and adapted to draw up crude oil therefrom. The pump unit comprises a pump cylinder, and a plunger reciprocatingly moved in the pump cylinder. The plunger is provided with a clearance formed between the outer circumferential surface of a lower end portion thereof and the inner circumferential surface of the pump cylinder. The pressure oil supplied from the hydraulic unit is ejected from the clearance along the inner surface of the pump cylinder into a cylinder chamber.

Abstract: A pumping system for oil production comprises a hydraulic unit set on the ground and adapted to send out a pressure oil, and a pump unit set in an oil well and adapted to draw up crude oil therefrom. The pump unit comprises a pump cylinder, and a plunger reciprocatingly moved in the pump cylinder. The plunger is provided with a clearance formed between the outer circumferential surface of a lower end portion thereof and the inner circumferential surface of the pump cylinder. The pressure oil supplied from the hydraulic unit is ejected from the clearance along the inner surface of the pump cylinder into a cylinder chamber.

Abstract: A high-speed bevel gear transmission system for transmitting power from an input shaft to a pair of parallel outputs shafts the axes of which intersect each other. The input shaft has a pair of driving bevel gears which are fixedly mounted thereon such that the driving bevel gears face in opposite directions and which have the same number and size of teeth spirally arranged in the opposite directions each other. The output shafts are supported on angular contact ball bearings and have two driven bevel gears fixedly mounted thereon which are engaged with the driving bevel gears. The speed transmission ratio of the output shafts to the input shaft is 1.45:1 to 0.476:0.1, the relation between a pressure angle .alpha. and helix angle .beta. of the driving bevel gears and driven bevel gears, and a pitch cone angle .delta. of the driven bevel gears are defined by the formula, R=[(tan.alpha..multidot.sin .delta.)/cos .beta.]-tan.beta..multidot. cos .delta. when 0.324.ltoreq.R.ltoreq.0.1.