The invention is in the field of hydraulic equipment. More particularly, the invention is a hydraulic cylinder designed to inwardly contain major portions of its control system. The cylinder furthermore includes a unique internal structure that optimizes the functionality of the unit. In a second embodiment of the invention, the cylinder is substantially self-contained and includes all of the components of the first embodiment, plus a fluid reservoir, a pump to pressurize the fluid, and a motor that drives the pump.
Complex hydraulic systems are often used in machines that must apply a large force to a load. Examples of machines of this type are earthmovers, such as front-end loaders and backhoes, and cranes. The hydraulic system functions to transfer power to various portions of the machine. Since these machines are typically used in harsh and/or remote locations, the machines must be reliable and easy to maintain.
A hydraulic system for a heavy-duty machine will usually include one or more linear actuators/hydraulic cylinders, a reservoir, and a high-capacity hydraulic pump that is driven by a powerful motor. The motor may also function to propel the machine. The operator of the machine controls the operation of the machine""s hydraulic components through the use of valves that affect the flow of hydraulic fluid to and from said components. The application of pressurized fluid to a hydraulic cylinder in a predetermined manner will cause the cylinder""s inwardly-contained piston to move within the body of the cylinder. As a result, the piston rod attached to the piston will be either extended from, or retracted into, the cylinder to cause the desired movement of the machine""s member(s) attached to the cylinder.
In a typical hydraulic system, the control valve that is responsible for the operation of any particular hydraulic cylinder is located at a distance from the cylinder. Long flexible hoses and/or pipes are used to connect together the control valve, the cylinder, the pump and the reservoir. Depending on the complexity of the system, additional hoses may be employed between main and pilot valves, and between system check valves and the control and/or pilot valve(s).
One problem with prior art hydraulic systems is that while most of a hydraulic system""s components are very durable, they are still susceptible to damage. By the time the pump, reservoir, valves and hydraulic cylinders are connected together, the end result is a large number of hoses, fittings, pipes and valves located in damage-prone areas. Many of these components are difficult and/or expensive to replace. One should also note that not only are the hoses susceptible to being punctured, they can also be damaged through environmental degradation.
Another problem with prior art hydraulic systems is leakage. Not only can each component of a hydraulic system leak, but the fittings that are used to connect together the different components can also leak. At the very least, leakage of hydraulic fluid can pose both safety and maintenance problems. If the machine is used in an environmentally-sensitive location, leakage problems are exacerbated since any leaked hydraulic fluid must be recovered, along with any contaminated soil.
In some hydraulic systems, the use of connecting hoses is minimized by mounting the hydraulic cylinder""s control valve, and in some cases, a pump and reservoir, directly onto the side of the hydraulic cylinder. However, this does not substantially avoid having hydraulic components located in an exposed condition where they can be damaged by falling debris or by accidental contact with external structure or formations. This also creates a bulbous, awkwardly-sized unit that cannot be fitted within the closely-packed confines found in many machines.
The invention is a hydraulic cylinder having a design optimized for durability, convenience and overall low cost. The cylinder may be employed in almost any machine in which a hydraulic cylinder is required. The invention is especially useful for employment in machines subject to hard usage and harsh environmental conditions, such as, but not limited to, earth-working machinery and cranes.
A hydraulic cylinder in accordance with the invention is similar in outward appearance to most standard hydraulic cylinders. However, the head portion of the cylinder, also known as a cylinder head, includes the cylinder""s main control valve. The cylinder head preferably further includes one or more electrically-actuated pilot valves and may include other ancillary components required to control fluid flow to internal areas of the cylinder, such as one or more pilot-operated check valves. In a second embodiment of the invention, the cylinder head also contains a fluid reservoir, pump and motor.
Like prior art hydraulic cylinders, the cylinder in accordance with the invention is elongated in shape and includes a movable piston attached to one end of a piston rod. However, to avoid the use of external structure and to make best use of the above-described structure of the cylinder head, a fluid transfer tube and hollow piston rod are employed within the cylinder. The tube extends from the cylinder head through the center of the piston and into the interior of the piston rod. The piston rod features at least one port located near the piston to enable fluid flow between the interior area of the piston rod and the interior area of the cylinder surrounding the piston rod. This creates an internal fluid path that extends from the cylinder head, through the transfer tube, through the interior of the piston rod, and then into an area of the cylinder surrounding the piston rod. In said area, the fluid can apply pressure to a first surface of the piston.
The cylinder head additionally includes a port through which fluid can be transferred directly from the cylinder head to an area located within the cylinder where the fluid can apply pressure to a second surface of the piston. The fluid flow to the above-noted port or to the transfer tube is controlled by the main control valve.
In the preferred embodiment, the main control valve is a spool-type valve that is preferably controlled by two pilot valves that are each operated by a dedicated solenoid. Both pilot valves and both solenoids are located in the cylinder head at a location where they are easily serviceable.
The electrical wiring to the solenoids extends out of the cylinder head and is operatively connected to a remotely-located control switch. In this manner, electrical actuation of the control valve structure may be achieved by an operator through actuation of a switch.
In a first embodiment of the invention, one hydraulic fluid supply line/hose is employed to connect the cylinder to a source of pressurized fluid, such as a pump. A second fluid return line/hose is used to connect the cylinder to a fluid reservoir. The latter line/hose inwardly contains the wires that connect the solenoids to the operator-actuated control switch and thereby also functions to protect the wires from damage.
To ensure the desired direction of fluid flow, the cylinder head preferably also includes two pilot-operated check valves. One valve is in the fluid path that leads to the cylinder area adjacent the first surface of the piston, and the other valve is in the fluid path that leads to the cylinder area adjacent the second surface of the piston. Preferably, when one pilot-operated check valve is opened to allow the flow of pressurized fluid, the other pilot-operated check valve will also be opened to provide a return path for displaced fluid. Also in the preferred embodiment, each of the pilot-operated check valves can be fluid locked into a closed position to maintain the piston in a stationary position when the control valve is in a neutral condition.
As noted previously, the second embodiment of the invention is a hydraulic cylinder that is substantially self-contained. This is achieved by including a fluid reservoir, pump, and motor within the cylinder head. As a result, no hydraulic lines extend outwardly from the cylinder. In a preferred form of this embodiment, the fluid reservoir is a cylindrical container. Preferably, the pump and motor are located within the reservoir where they can be cooled by the fluid within the reservoir.
The reservoir also functions to maintain pressure on the contained fluid and can expand or contract in order to accommodate changes in the amount of fluid contained within the reservoir. In the preferred embodiment, this is achieved by the inclusion of an expansible or movable portion of the reservoir, such as a bellows, elastic bag or piston that enhances the ability of the reservoir to expand or contract.
By encasing the hydraulic cylinder""s main control valve and other fluid-related components within the cylinder head, the components are protected from damage. Also, in the embodiments of the invention described herein, many or all of the exterior hoses and fittings required for the hydraulic system are eliminated. As a result, the invention provides a hydraulic cylinder that avoids most of the problems of the prior art. Furthermore, the hydraulic cylinder has a shape and space envelope similar to most conventional units. In many cases, this allows the invention to be directly substituted for a conventional hydraulic cylinder.