FIELD OF THE INVENTION

This invention relates generally to the field of high-low hydraulic systems used in balers, compactors, transfer station compactors, and the like.

BACKGROUND

Hydraulic systems used within compacting machinery, which compresses material, often comprising of a variety of objects (e.g., trash, cardboard boxes and etc.), into a compacted bundle for easier handling, transport, and storage, are well known. In basic form, such hydraulic systems operate a cylinder, which provides a reciprocating piston. Hydraulic systems used in compacting machinery often utilize a double rotary pump comprising a big displacement pump and a small displacement pump as well as a plurality of directional control valves. Each pump produces a flow that is directionally controlled by the plurality directional control valves within the hydraulic system. Such hydraulic systems are commonly referred to as a high-low hydraulic system.

The cylinder comprises a tubular housing that substantially encloses the piston. The piston is capable, when actuated, of translating within the tubular housing in two directions. The piston extends outward to compress the material and retracts inward to release the material. The piston comprises a blind end side and a rod end side. The extension of the rod and piston is referred to as a compaction stroke and the retraction of the rod and piston is referred to as a retraction stroke. The compaction stroke may be a high-pressure stroke and the retraction stroke is a low-pressure stroke.

Conventionally, at low-pressure, the piston within the cylinder retracts at a high speed because flow from the big and small displacement pumps is concurrently directed to the cylinder. Conversely, at high-pressure, the piston within the cylinder extends at a low speed because only flow from the small displacement pump is directed to the cylinder. When the cylinder is operating under a high-pressure state, the flow from the big displacement pump is directed to a tank by the use of an unloading valve. Before the piston begins to retract, the hydraulic fluid on its blind end side is decompressed by a directional solenoid valve which allows the hydraulic fluid on the blind end side to return to tank. Accordingly, conventional high-low hydraulic systems decompress the hydraulic fluid on the blind end side of the piston such that the retraction stroke of the piston is delayed until decompression is completed.

Conventional high-low hydraulic systems, at the onset of the compaction stroke, direct the combined flow from the big and small displacement pumps to the cylinder which results in a hydraulic shock that often produces a loud bang. The hydraulic shock, which results from a large pressure spike, can reduce the service life of the compacting machinery. Such rapid accumulation of pressure can be damaging to the cylinder and other components of the hydraulic system. Furthermore, conventional high-low hydraulic systems cannot operate the cylinder at two or more independent speeds, in both directions, at a pressure lower than a pressure setting of an unloading valve that is fluidly coupled to the big displacement pump.

Accordingly, this invention improves the performance of conventional high-low hydraulic systems, whether regenerative or non-regenerative, that are used within compacting machinery, by cleverly controlling flow such that the hydraulic shocks arising at the beginning and end of the compaction and retraction strokes are significantly mitigated. Further, this improved high-low hydraulic system allows the piston to operate at least three independent speeds and increases the system efficiency.

SUMMARY OF THE INVENTION

The present invention provides an improved high-low hydraulic system used for compacting machinery, such as balers, horizontal balers, compactors, transfer station compactors, and the like. Such compacting machinery with hydraulic systems, in general, utilize one or more double rotary pumps in fluid communication with a cylinder to extend and retract the cylinder for the purpose of compacting one or more items.

The high-low hydraulic system, in basic form, comprises a tank, a cylinder, a plurality of one-way valves, a plurality of pressure gauges and pressure switches, at least one flow control valve, at least one strainer, at least one return line filter, a pilot-operated back pressure reducing valve, a plurality of directional control valves, and a double rotary pump which is further comprised of a big displacement pump and a small displacement pump, each with an inlet and outlet.

The cylinder has a first end and a second end. The cylinder comprises a rod, piston, and cylinder housing. The piston has a blind end side, which is substantially adjacent to the first end of the cylinder, and a rod end side, which is substantially adjacent to the second end of the cylinder. The cylinder is actuated (i.e., translated) via fluid pressure, alternatively sometimes referred to herein as “hydraulic pressure”, generating differential resultant forces acting on opposing sides of the piston.

The plurality of directional control valves comprises at least one solenoid-controlled, pilot-operated directional control valve, hereinafter the “two-stage DCV.” Each two-stage DCV has a main section and a pilot section. The main section, being pilot-operated, is fluidly connected to the pilot section by two pilot lines. The two-stage DCV provides a pressure port which is fluidly connected to the main section and the outlet of the big displacement pump. The pilot section has an inlet that is connected to a pilot pressure line which fluidly connects the outlet of the small displacement pump to the pilot section. Each two-stage DCV further comprises six ports. The six ports further comprising the pressure port (“P”), a tank port (“T”), two actuator ports (“A” and “B”), a pilot pressure port (“X”), and a pilot drain port (“Y”).

The high-low hydraulic system is configured such as to assist with the mitigation of hydraulic shocks from developing within the cylinder by the cleverly sequencing flow from the big and small displacement pumps to the cylinder during the compaction stroke as well as cleverly diverting flow from the blind end side during decompression via the at least one metered-out flow control valve and, at the end of decompression, by way of the pilot-operated back pressure reducing valve. The clever flow sequencing also allows for a reduced cycle time, which comprises the time required to complete one compaction stroke and one retraction stroke, as a result of the high-low hydraulic system directing flow from the small displacement pump to the rod end side during decompression. Additionally, the clever flow sequencing allows for the cylinder to be operated at three or more independent speeds.

A regular output of the pilot-operated back pressure reducing valve is fluidly connected to the “A” port of the two-stage DCV and the regular input of the pilot-operated back pressure reducing valve is fluidly connected to the tank. The pilot line of the pilot-operated back pressure reducing valve is directly connected to an output of the “B” port of the each two-stage DCV. Additionally, it is anticipated that return lines of the directional control valves, which are fluidly coupled to “T” port of each directional control valve, may be connected to pressure ports of additional directional control valves if the high-low hydraulic system comprises additional auxiliary cylinders.

To reverse the motion of the piston without a significant hydraulic shock, flow from the small displacement pump is first directed to the cylinder to provide a piston speed. Then after a first predetermined time has passed, flow from the outlet of the big displacement pump is directed to the same side of the piston as flow from the outlet of the small displacement pump, thereby producing a combined maximum flow.

When the elastic load is present during the compaction stroke, the system pressure required to continue extending the piston will increase as the piston extends. The motor provides a maximum allowable power which governs a maximum allowable pressure that the hydraulic system is capable of producing when operating at a given flow. The pressure switch which is fluidly connected to the outlet of the big displacement pump provides a pressure setting that automatically de-energizes the two-stage DVC when the system pressure is substantially at or above a predetermined first maximum allowable pressure. Accordingly, after the hydraulic pressure on the blind end side reaches the predetermined first maximum allowable pressure, flow from the outlet of the big displacement pump is unloaded to tank.

Accordingly, the piston is able to continue extending, albeit at a lower speed, due to only the flow from the small displacement pump being directed to the blind end side. Finally, after the hydraulic pressure on the blind end side reaches a predetermined second maximum allowable pressure, which is greater in magnitude relative to the predetermined first maximum allowable pressure, the pressure switch (or transducer) that is fluidly connected to the outlet of the small displacement pump provides a second pressure setting which either initiates decompression of the blind end side or de-energizes the directional control valve that controls the flow from the outlet of the small displacement pump, which results in the fluid isolation of the cylinder and the double rotary pump. Both the blind end side and rod end side of the piston may be isolated from the tank and the double rotary pump if the directional control valves, which each side is respectively fluidly coupled to, are in a neutral, de-energized state. To mitigate a significant hydraulic shock, and a corresponding loud bang, from developing during decompression of the blind end side at the end of the compaction stroke, the metered-out flow control valve is utilized to control the rate at which decompression occurs. The pilot-operated back pressure reducing valve further improves system efficiency as it is automatically opened without requiring additional energy for its operation when a predetermined pilot ratio is reached. The predetermined pilot ratio comprises a predetermined ratio of the hydraulic pressure within the output lines of the “A” port of each two-stage DCV to the hydraulic pressure within the output lines of the “B” port of each two-stage DCV.

At the onset of decompressing the blind end side, flow from the outlet of the small displacement pump is directed to the rod end side. After a second predetermined time, relative to the start of decompression, flow from the outlet of the big displacement pump is temporarily directed to the rod end side to reduce the time retraction. Flow from the outlet of the big displacement pump is subsequently directed to tank after a third predetermined time to substantially avoid a hydraulic shock at the end of the retraction stroke from developing.

Alternatively, a similar configuration of the improved high-low hydraulic system may be provided without the one or more regenerative blocks. Consequently, output lines from the “A” port of the directional control valves would be directly fluidly connected to each other and to the blind end side of the piston, while the output lines from the “B” ports of the directional control valves would be fluidly connected to each other and to the rod end side of the piston.

