Abstract: A method and apparatus for vertically adjusting the stroke of the polished rod of a pumpjack during its operation in a producing well, while detecting abnormal conditions such as gas-off, pump seizure, sucker and separation, gas-lock pounding or fluid pounding. The method and apparatus involves a hydraulic or pneumatic cylinder interposed between the polished rod clamp and the carrier bar of the pumpjack. Abnormal conditions are detected by an electronic device incorporating a pressure transducer which senses fluid pressure changes in the hydraulic or pneumatic cylinder, converts the pressure changes into electrical voltages, and then determines if an abnormal condition is present. If an abnormal condition is sensed, the pumpjack can be stopped, and restarted automatically after a momentary interval in the event of gas-lock or fluid pounding, or manually after inspection by an operator in the event of a more serious condition.

Abstract: A differential gear includes a differential case having a plurality of recesses provided circumferentially at equal intervals, a plurality of pinions and a pair of side gears respectively disposed in the differential case, shafts connected to the respective side gears and a sleeve supported by one shaft shiftably in an axial direction thereof and unrotatably relative thereto and having a plurality of claws capable of fitting in the recesses. A controlling device includes a cylinder unit for operating the sleeve, a pressure sensor for detecting the braking condition of a vehicle, a sensor for detecting a steering angle and a controller for receiving signals from both sensors and controlling the cylinder unit to limit the rotational speed differential generated from the the differential gear when the vehicle is braked and turned with a steering angle exceeding a predetermined value.

Abstract: A reciprocating drive mechanism powered by a rotating prime mover for use, for example, in operating oil well pumps. The drive mechanism utilizes a rotating pinion meshing with an endless arcuate rack gear to convert rotation to reciprocation and includes an assembly to provide a positive engagement between the pinion and rack gear. The prime mover is coupled to a fixed input shaft, the input shaft has the pinion coupled thereto, and an endless arcuate rack gear is rigidly coupled to an output shaft and meshes with the pinion. An arcuate cam is rigidly coupled to the arcuate rack gear and is engaged by a pair of cam followers which are also coupled to the pinion. A transmission shaft, which supports the pinion and cam followers, is parallel to and located a fixed distance from the input shaft, thereby maintaining the cam followers in positive engagement with the cam and the pinion in positive engagement with the rack gear.