System and method for controlling motor torque

#The present invention is directed to a system and method for controlling a motor torque output. More particularly, the invention relates to a system and method for controlling a motor torque output by monitoring an operating condition of a hydrostatic motor.

#A pump having a variable displacement capability is well known in the industry to drive a hydrostatic motor. In a machine having a variable displacement pump and a hydrostatic motor, such as an excavator or a loader, the pump provides fluid to the hydrostatic motor and drives the motor in the forward or reverse direction. The speed of the hydrostatic motor is controlled by varying the displacement of the pump.

#A variable displacement pump generally includes a drive shaft, a rotatable cylinder barrel having multiple piston bores, pistons held against a tiltable swashplate, and a valve plate. When the swashplate is tilted relative to the longitudinal axis of the drive shaft, the pistons reciprocate within the piston bores to produce a pumping action. Each piston bore is subject to intake and discharge pressures during each revolution of the cylinder barrel.

#The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description, serve to explain the principles of the invention.

#FIG. 1 is a schematic and diagrammatic representation of a machine having a system for controlling a motor torque output according to one exemplary embodiment of the present invention;

#FIG. 2A is a diagrammatic representation of a valve face of a hydrostatic motor overlying a cylinder barrel and having piston ports at the BDC position;

#Reference will now be made in detail to exemplary embodiments of the invention, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

#FIG. 1 schematically and diagrammatically illustrates a machine having a system for controlling motor torque output according to one exemplary embodiment of the invention. The machine 10 shown in FIG. 1 may be an excavator, a loader, or any other piece of equipment utilizing a hydraulic system.

#The machine 10 includes a pump 12 typically driven by an engine 14, such as an internal combustion engine, via a drive train 16. In an exemplary embodiment, the pump 12 is a variable displacement pump and can vary its displacement between minimum and maximum displacement positions. Typically, the pump 12 includes pump ports 15, a drive shaft (not shown), a rotatable cylinder barrel having multiple piston bores (not shown), and pistons held against a tiltable swashplate (not shown). The swashplate is tilted relative to the longitudinal axis of the drive shaft, and the pistons reciprocate within the piston bores to produce a pumping action. One skilled in the art appreciates the basic structure of a variable displacement pump, and the structure will not be described or shown in detail.