| 摘要 |
A hydraulic drive system for actuating a reciprocating member such as a polished rod in a pump jack device, and for acting as a counterbalance and/or for energy conservation. The system has two hydraulic circuits and a prime mover. A first circuit includes a cylinder for driving an output member which may be connected to the polished rod, a first pump of the variable displacement, reversible flow type, together with a pair of fluid lines forming with the cylinder a closed-loop circuit. A controller is programmed to control the setting of the first pump so as to establish the velocity profile of the output member. A second hydraulic circuit is also in the form of a closed-loop containing first and second pumps, at least one of which is of the variable displacement type and is also controlled by the controller. The second and third pumps at least are of the pump/motor types, and the third pump has an input/output shaft connected to a flywheel so that as the third pump is driven as motor, it increases the speed of the flywheel. However, when the second circuit is controlled so that the second pump functions as a motor and the third pump functions as a pump, energy is extracted from the flywheel so that its RPM decreases. The first pump is driven by the prime mover, and the second pump, which can drive the first pump when it is functioning as a motor, may alternatively be driven by the prime mover as well or by both the prime mover and the first pump, if the latter functions as a motor, such as during the down stroke of the polished rod.
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