Hydraulic drive circuit for machine tools

Claim 2

A fluid drive for double acting piston and cylinder power rams which comprises conduits supplying and draining fluid from opposite ends of the ram cylinder on opposite sides of the piston therein to alternately drive the piston to opposite ends of the cylinder, a pump supplying fluid to said conduits, a reservoir receiving fluid from said conduits, a reversing valve controlling the direction of flow of fluid through the conduits, an accumulator communicating with one of the conduits to maintain a predetermined fluid pressure therein, a sequence unloading valve in said one conduit unloading the pump whenever fluid pressure in the conduit is above a predetermined maximum controlled by said accumulator, a relief valve set to open at a higher pressure than said sequence unloading valve communicating with the pump discharge, a dump valve for said accumulator, and means biasing said reversing valve to flow fluid through the conduits for holding the piston in the power ram at one end of its stroke until the reversing valve is actuated against the bias to flow fluid for driving the piston to the other end of its stroke to deliver power.

Claim 3

In a machine tool having a twin cylinder actuated member with each cylinder having a piston linked to the member to raise the member to an idle position and to drive the member downwardly through a power stroke, the improvement which comprises a hydraulic circuit for said twin cylinders including conduits supplying fluid to opposite ends of each cylinder to raise and lower the pistons, a reversing valve controlling the direction of flow of the fluid through the conduits, a positive displacement pump supplying fluid through the reversing valve to the conduits, a relief valve for said pump, an accumulator communicating with a conduit for raising the pistons, a sequence unloading valve controlled by accumulator pressure to unload the pump below a maximum pressure, a dump valve for said accumulator, and means biasing said reversing valve to a position for flowing fluid from the pump to the accumulator and to the bottoms of the cylinders for raising the pistons, and manually actuated means for shifting the reversing valve against the bias to flow fluid to the tops of the pistons and deliver a power stroke to the member whereby the member will normally be raised and held in a raised position until the reversing valve is actuated to deliver the power stroke.

Claim 4

In a machine tool having a twin cylinder actuated member with each cylinder having a piston linked to the member to raise the member to an idle position and to drive the member downwardly through a power stroke, the improvement which comprises a hydraulic circuit for said twin cylinders including conduits supplying fluid to opposite ends of each cylinder to raise and lower the pistons, a reversing valve controlling the direction of flow of the fluid through the conduits, a positive displacement pump supplying fluid through the reversing valve to the conduits, a relief valve for said pump, an accumulator communicating with a conduit for raising the pistons, a sequence unloading valve controlled by accumulator pressure to unload the pump below a maximum pressure, a dump valve for said accumulator, and means biasing said reversing valve to a position for flowing fluid from the pump to the accumulator and to the bottoms of the cylinders for raising the pistons, and manually actuated means for shifting the reversing valve against the bias to flow fluid to the tops of the pistons and deliver a power stroke to the member whereby the member will normally be raised and held in a raised position until the reversing valve is actuated to deliver the power stroke.

Claim 5

In a power shear having an upstanding reciprocating blade carrier, links depending from the ends of the blade carrier, a rotatable torsion rod having levers projecting from the ends thereof pivoted to said links, and twin double acting cylinders pivoted to the ends of the levers beyond the links for swinging the levers to rotate the torsion bar and raise and lower the links for reciprocating the blade carrier, the improvement of a hydraulic circuit for operating said twin cylinders having conduits communicating with the tops and bottoms of the cylinders, a pump for flowing fluid through the conduits to raise and lower the pistons in the cylinders, a reversing valve controlling the direction of flow through the conduits, an accumulator maintaining fluid in the bottoms of the cylinders, an unloading valve for recirculating fluid from the pump whenever fluid pressure in the accumulator exceeds a predetermined maximum, and a relief valve for the pump in advance of the unloading valve to dump pump pressure when the blade carrier reaches the bottom of its stroke, whereby the blade carrier will be urged to a raised position by accumulator pressure and will be forced downwardly through a power stroke only when the reversing valve delivers fluid to the tops of the cylinders.

Claim 6

In a power shear having an upstanding reciprocating blade carrier, links depending from the ends of the blade carrier, a rotatable torsion rod having levers projecting from the ends thereof pivoted to said links, and twin double acting cylinders pivoted to the ends of the levers beyond the links for swinging the levers to rotate the torsion bar and raise and lower the links for reciprocating the blade carrier, the improvement of a hydraulic circuit for operating said twin cylinders having conduits communicating with the tops and bottoms of the cylinders, a pump for flowing fluid through the conduits to raise and lower the pistons in the cylinders, a reversing valve controlling the direction of flow through the conduits, an accumulator maintaining fluid in the bottoms of the cylinders, an unloading valve for recirculating fluid from the pump whenever fluid pressure in the accumulator exceeds a predetermined maximum, and a relief valve for the pump in advance of the unloading valve to dump pump pressure when the blade carrier reaches the bottom of its stroke, whereby the blade carrier will be urged to a raised position by accumulator pressure and will be forced downwardly through a power stroke only when the reversing valve delivers fluid to the tops of the cylinders.

Claim 7

The fluid drive of claim 1, wherein said reversing valve is biased to one flow through position and is manually actuated to an opposite flow through position.

Claim 8

The fluid drive of claim 1, wherein the accumulator accepts fluid flow at pressures above its setting to deliver the fluid when needed.

Claim 9

The fluid drive of claim 1, wherein the pump is a fixed displacement pump, the accumulator maintains a back pressure of about 500 pounds per square inch, and the relief valve is set to open at pressures above 2,000 pounds per square inch.

Claim 10

The machine tool of claim 2, wherein the reversing valve is biased to one flow through position and is manually actuated against the bias to a second flow through position, whereby fluid will flow through the valve under all operating conditions.

Claim 11

The machine tool of claim 2, including a check valve in the hydraulic circuit preventing back flow from the accumulator to the pump.

Claim 12

The machine tool of claim 2, wherein the twin cylinder actuated member is an upstanding reciprocating member held in a raised position until the reversing valve is manually actuated.

Claim 13

The power shear of claim 3, including a check valve stopping flow from the accumulator to the pump and effective to maintain accumulator pressure under the pistons.

Claim 14

The power shear of claim 3, including switches tripped by the blade carrier at the top and bottom of its stroke controlling the reversing valve to determine the length of the blade carrier stroke.

Claim 15

The fluid drive of claim 1, including an electrical circuit actuating said reversing valve to reverse the direction of flow of fluid through the conduit before the piston impacts against the opposite ends of the cylinder.

Claim 16

The fluid drive of claim 1, including an electrical control circuit actuating the reversing valve against the biasing means and having trip switches alternately opened and closed before the piston impacts against the ends of the cylinder to reverse fluid flow.

Claim 17

The machine tool of claim 2, including an electrical circuit energized through said manually actuated means for shifting the reversing valve and having trip switches activated by the twin cylinder actuated member at the top and bottom of its stroke to prevent the pistons from impacting against the ends of the cylinders.

Claim 18

The machine tool of claim 14, including a relay in the circuit effective to cycle the member through a plurality of strokes until the manually actuated member is released.