Hydraulic pumps compress and move hydraulic fluids by mechanical action in order to generate and transmit power. In hydraulic tool systems, hydraulic pumps provide high-pressure fluid to various actuators that transmit forces necessary to perform work. The actuators of such hydraulic tool systems often require that hydraulic fluid be provided at different flow rates and pressures for proper function. Variable displacement pumps can be utilized to accommodate the varied flow rate and pressure requirements, both individually and collectively, of the multiple actuators of hydraulic tool systems.
Swashplate-type axial piston pumps are variable displacement pumps commonly used in hydraulic tool systems. Swashplate-type axial piston pumps include a plurality of plungers having one end held against an engagement surface of a tiltable swashplate. A ball-and-socket slipper joint is provided at the interface between each plunger end and the engagement surface of the swashplate to allow for relative sliding and pivoting motion. Each plunger reciprocates within an associated cylinder as the plungers rotate relative to the tilted engagement surface of the swashplate. When a plunger is retracted from an associated cylinder, low-pressure fluid is drawn into that chamber. When the plunger is forced back into the cylinder by the engagement surface of the swashplate, the plunger pushes fluid from the cylinder at an elevated pressure.
Each cylinder and associated plunger together at least partially form a pumping chamber configured to intake hydraulic fluid from an inlet passage and to discharge hydraulic fluid into an outlet passage. Each pumping chamber interfaces with the inlet passage and the outlet passage through a port plate. The port plate includes an inlet port through which hydraulic fluid is drawn from the inlet passage into the pumping chamber and an outlet port through which hydraulic fluid is expelled from the pumping chamber into the outlet passage. As a plunger of a pumping chamber moves from a top-dead-center (TDC) position at the end of a discharge stroke to a bottom-dead-center position at the end of an intake stroke, the plunger passes the inlet port as it rotates relative to the port plate. As a plunger of a pumping chamber moves from a bottom-dead-center (BDC) position at the end of an intake stroke to a top-dead-center position at the end of a discharge stroke, the plunger passes the outlet port as it rotates relative to the port plate.
The tilt angle of the swashplate is directly related to an amount of fluid pushed from each cylinder during a single relative rotation between the plungers and the swashplate. Similarly, based on a restriction of a fluid circuit connected to the pump, the amount of fluid pushed from the cylinder during each rotation is directly related to the flow rate and pressure of fluid exiting the pump. Accordingly, a higher swashplate tilt angle of a pump equates to a greater flow rate and/or pressure of the pump, while a lower swashplate tilt angle results in a lower flow rate and/or pressure. Likewise, a higher swashplate tilt angle requires more power to produce the higher flow rates and pressures than does a lower swashplate tilt angle. As such, when the demand for fluid from the hydraulic tool system is low, the swashplate angle is typically reduced to lower the power consumption of the pump.