Variable displacement pump control system

Claim 2

A hydraulic system comprising: a main variable displacement hydraulic pump having an inlet line and a discharge line; a pump regulating means responsive to pressure in a pump regulating line to respectively decrease or increase pump displacement in response to an increase or decrease in the pump regulating line pressure; a charge pump means having an inlet line connected to a reservoir and an outlet line connected to the main pump inlet line for supplying fluid thereto; a pilot-operated stroke control valve means connected to the reservoir, the charge pump outlet line and the regulating lines; means biasing the valve toward a first position wherein it connects the pump regulating line to the reservoir to decrease the pressure therein and increase the pump displacement; and a first pilot line operatively connected to the stroke control valve and the main pump discharge line for shifting the valve against said biasing means when the force exerted by fluid pressure in the pilot line exceeds the force exerted by the biasing means into a second position wherein it connects the charge pump outlet line to the pressure regulating line to increase the pressure therein and reduce the pump displacement.

Claim 3

The invention defined in claim 1 and including at least one hydraulic function and the biasing means includes a second pilot line operatively connected to the hydraulic function and the stroke control valve for applying the fluid pressure in the hydraulic function to the stroke control valve in opposition to the first pilot line, so that the valve shifts to its second position when the pressure in the discharge line exceeds the pressure in the hydraulic function by a predetermined amount.

Claim 4

The invention defined in claim 2 and including a bleed line having a flow restricting orifice connecting the second pilot line to the reservoir.

Claim 5

The invention defined in claim 1 and including a pressure regulating valve operatively associated with the charge pump outlet line for maintaining a predetermined pressure in the outlet line.

Claim 6

A hydraulic system comprising: a main variable displacement hydraulic pump having a plurality of cylinders with inner ends opening into a closed drive chamber and closed outer ends connected to an inlet line and a discharge line, a piston mounted in each cylinder and drive means within the chamber engageable with the inner ends of the pistons to reciprocate the pistons, the pressure in the inlet line returning the pistons into driving engagement with the drive means and the pressure in the chamber opposing said engagement, so that the piston strokes are dependent upon the relative pressures in the inlet line and the drive chamber; a pump regulating line connected to the drive chamber; a charge pump having an outlet line connected to the main pump inlet line for supplying pressurized fluid to the outer ends of the cylinders; a pilot-operated stroke control valve shiftable between a first position, wherein it connects the pump regulating line to the reservoir to decrease the pressure in the drive chamber and increase the piston strokes, and a second position, wherein it connects the pump regulating line to the charge pump discharge line to increase the pressure in the drive chamber and decrease the piston strokes; means biasing the stroke control valve toward its first position; and a pilot line between the main pump discharge line and the sroke control valve for applying the discharge line pressure to the valve opposite the biasing means to shift the valve into its second position when the force exerted by the pilot line pressure exceeds the force exerted by the biasing means.

Claim 7

A hydraulic system comprising: a main variable displacement hydraulic pump having a plurality of cylinders with inner ends opening into a closed drive chamber and closed outer ends connected to an inlet line and a discharge line, a piston mounted in each cylinder and drive means within the chamber engageable with the inner ends of the pistons to reciprocate the pistons, the pressure in the inlet line returning the pistons into driving engagement with the drive means and the pressure in the chamber opposing said engagement, so that the piston strokes are dependent upon the relative pressures in the inlet line and the drive chamber; a pump regulating line connected to the drive chamber; a charge pump having an outlet line connected to the main pump inlet line for supplying pressurized fluid to the outer ends of the cylinders; a pilot-operated stroke control valve shiftable between a first position, wherein it connects the pump regulating line to the reservoir to decrease the pressure in the drive chamber and increase the piston strokes, and a second position, wherein it connects the pump regulating line to the charge pump discharge line to increase the pressure in the drive chamber and decrease the piston strokes; means biasing the stroke control valve toward its first position; and a pilot line between the main pump discharge line and the sroke control valve for applying the discharge line pressure to the valve opposite the biasing means to shift the valve into its second position when the force exerted by the pilot line pressure exceeds the force exerted by the biasing means.

Claim 8

The invention defined in claim 5 and including at least one hydrualic function, the biasing means including a second pilot line operatively connected to the hydraulic function and the stroke control valve for applying the fluid pressure in the hydraulic function to the stroke control valve in opposition to the first pilot line, so that the valve shifts to its second position when the pressure in the discharge line exceeds the pressure in the hydraulic function by a predetermined amount.

Claim 9

The invention defined in claim 6 and including a bleed line having a flow restricting orifice connecting the second pilot line to the reservoir.

Claim 10

The invention defined in claim 5 and including a pressure regulating valve operatively associated with the charge pump outlet line for maintaining a predetermined pressure in the outlet line.

Claim 11

The invention defined in claim 5 wherein the piston and cylinder extend radially from the pump axis and the drive means comprises a cylindrical member eccentrically disposed relative to the pump axis.