The present invention concerns an energy efficient hydraulic cylinder in accordance with the claims. The patent application also concerns the use of a hydraulic cylinder. Background of the Invention and Prior Art

In connection with lifting loads by various types of lifting equipment such as cranes, construction machinery and the like, a large amount of energy is used to change both the position of the lifting device's mass and the position of the mass of the lifted load. A great deal of energy is consumed just for changing the position of the lifting device's mass. The energy consumed to lift for example the weight of a crane or similar, is not reused but is lost as heat generation and the like. There is a need for an energy efficient system to raise and lower loads with cranes and construction machinery.

Many types of devices have been developed in order to reduce energy losses associated with vertical position changes of loads and the like. For example, different types of hydraulic cylinders and similar have been developed which are designed to reduce energy losses when lifting devices perform positional changes. One example of such a hydraulic cylinder, for use in lifting and lowering a component, is described in patent application SE461391 of applicant BT Industries. The cylinder described in the application is of a double-acting type. The uniqueness of hydraulic cylinders, which are of a double-acting type, is that they include a piston rod which is hollow that forms an inner pumping chamber in the piston rod. The design includes a variant of a second piston which in its one end is connected to the working cylinder and in its other end is movably arranged relative to the inner chamber of the piston rod. This design differs greatly from the design of the present invention. For example, the second piston is not movably arranged in relation to both the working cylinder and the piston rod. Further, the compressed medium in the inner chamber of the piston rod consists of air.

Furthermore, a hydraulic cylinder which includes an inner chamber in the piston rod is known via patent document US7478489. Patent document US7478489 describes a variant of a working cylinder with a piston rod that includes an inner chamber in which a fluid is compressed. This design differs substantially from the present invention. For example, it does not include a moveable second piston in accordance with the design according to the present patent application. A working cylinder which includes an inner chamber in the piston rod in which a liquid is arranged to be compressed is also described in patent document US7441405. Even this design differs substantially from the present invention. For example, it does not include a moveably arranged second piston in accordance with the present invention. Patent document DEI 02007061294 describes a variant of a hydraulic cylinder including three lift chambers. The design includes a working cylinder in the piston rod. Even this design differs substantially from the design in accordance with the present invention. For example, it does not include a moveably arranged second piston in accordance with the present invention.

Another variant of a hydraulic cylinder which includes a piston rod with an inner chamber is known from patent document DEI 02004044962. Even this design differs substantially from the design in accordance with the present invention. For example, it does not include a moveably arranged second piston in accordance with the present invention.

Brief Description of the Invention Concept

The main purpose of the design according to the present invention is to create a more energy efficient hydraulic cylinder than previously known designs. Another purpose of the present invention is to create a highly efficient hydraulic system, which to a large extent can be built with simple and reliable components. It is also an aim of the present invention that the hydraulic cylinder can be advantageously used for maneuvering (operating) the lifting arms and bucket of a wheel loader or similar heavy equipment as well as cranes and the like. Detailed Description of the Invention

The invention will be described in greater detail below with reference to the accompanying schematic drawings that in an exemplifying purpose show the current preferred embodiments of the invention.

Figure 1 shows a first embodiment of the hydraulic cylinder in accordance with the present invention.

Figure 2 shows a cross-sectional view, from A to A in figure 1 , of a hydraulic cylinder in accordance with the present invention.

Figure 3 shows in a hydraulic diagram an example of use of the hydraulic cylinder in accordance with the present invention. Figure 4 shows in a second hydraulic diagram a second example of an application for the present hydraulic cylinder.

Figure 5 shows in a third hydraulic diagram a third example of an application for a hydraulic cylinder in accordance with the present invention. With reference to figure 1 , an exemplifying version of a hydraulic cylinder 1 is schematically shown in accordance with the present invention. The exemplifying hydraulic cylinder's design is only one of the possible embodiments for how a hydraulic cylinder according to the present invention can be designed. Hence the shown hydraulic cylinder is not a limitation for the design of a hydraulic cylinder in accordance with the present invention. The hydraulic cylinder 1 is, in its fundamental design, based upon some previously known hydraulic cylinder which has been modified in accordance with the present invention. The hydraulic cylinder (working cylinder) 1 includes a cylinder housing 2 and in it one movable piston 3. Preferably, the cylinder housing 2 includes a cylinder 4, a first end 5 and a second end 6. The piston 3 includes a piston head 7 (or similar) and at least one piston rod 8. The piston rod 8 runs through a hole (lead-through) in the end 6 in accordance with previously know technical solutions. The first end 5 and the cylinder 4 may either be separate or integrated with one another. Furthermore, the second end 6 and the cylinder 4 may either be separate or integrated with one another.

The piston head 7 separates the inner chamber of the cylinder housing into at least one first chamber 9 and at least one second chamber 10. The first chamber 9 is provided with at least one connection 11 to which the first chamber in the hydraulic cylinder can be connected to a hydraulic circuit system. The second chamber 10 is provided with at least one second connection 12 such as a connection or the like with which the hydraulic cylinder's second chamber can be connected to a hydraulic circuit (hydraulic system, hydraulic circuit system). Connection of the hydraulic cylinder 1 to the hydraulic system and pressurization of each respective chamber 9 and 10 is done in accordance with previously known technology and this is why this technique is not described in more detail in this patent application. The piston 3 will however move in a direction relative to the cylinder where a lesser force (surface times pressure) works against the piston surface. Preferably, the cylinder housing 2 further includes at least one mounting attachment 13 or the like with which the cylinder housing can be attached (connected) to an object or the like. In the shown embodiment the mounting attachment 13 and the end 5 consist of an integrated unit. The piston rod 8 includes a mounting attachment 14 or similar with which the piston rod, from the cylinder housing's protruding part, can be attached (connected) to an object in a for the purpose suitable manner. The mounting attachment 13 in the cylinder housing and the mounting attachment 14 in the piston rod consist of a variant of previously known types of mounting attachments which are suitable for the purpose. For example, the mounting attachment 13 and the mounting attachment 14 may consist of a handle (eye) or other previously known for the purpose suitable type of mounting attachment.

A unique feature of the present invention is that the piston rod 8 in the axial direction is provided with an inner chamber 15 which forms a space in which a liquid such as hydraulic oil or similar can be compressed by at least one second piston 16. The inner chamber 15 is preferably cylindrical with an axial center essentially parallel with the piston rod's 8 axial center. The inner cylindrical chamber's 15 axial center essentially coincides with the piston rod's axial center. The piston 16 is movably arranged in relation to the inner chamber 15. During movement of the piston 16 in the direction into the inner chamber 15, a compression of the fluid in the inner chamber of the piston will occur.

A unique feature of the present invention is that the second piston 16 is arranged to be moveable in the inner chamber 15. Further, the piston 16 is free to move relative the cylinder 4 and in relation to the end 5. A uniqueness of the present invention is that the piston runs freely in the essentially cylindrical inner chamber 15 in the piston rod 8 and that the piston is moveably arranged relative the cylinder housing and the cylinder end 5. The length and form of the piston 16 may vary greatly within the scope of the present invention. Figure 2 shows a piston 16 which has the same diameter. In alternative embodiments it is conceivable that the second piston's diameter varies along its longitudinal direction. The inner cylindrical chamber 15 is via at least one connection 17 attached to a hydraulic circuit, hydraulic system or the like. The connection 17 consists of previously known attachment devices such as for example a hydraulic coupling.

The hydraulic cylinder 1 includes the necessary seals (packing) so that satisfactory seals between the piston head and the cylinder housing and between the second piston 16 and the walls in the inner chamber 15 are achieved.

During the pressurization of fluid in the hydraulic cylinder's 1 first chamber 9, the first piston 3 strives to move itself so that the chamber 9 lengthens in the hydraulic cylinder's longitudinal direction. During the pressurization of fluid in the hydraulic cylinder's 1 first chamber 9, the second piston 16 strives to move by the force pressing against the second piston's 16 surface 18. The second piston 16 will through force of pressure in the hydraulic cylinder's 1 first chamber 9, pressing against the piston's surface 18 strive to compress the fluid in the inner cylindrical chamber 15 via the piston's second surface 19. Movement of the second piston 16 into the inner chamber 15 will occur under the condition that an outflow of fluid (hydraulic oil) can take place via connection 17. If surface 18 and surface 19 are the same the piston will move in the direction into the chamber (the inner cylindrical chamber 15 or the first chamber 9) where a lesser pressure prevails (under the condition that an amount of oil moves out via the connection 1 1 or 17).

The present hydraulic cylinder's design allows for the surface 20 on the piston head in the direction towards the chamber 9 and the second piston's surface 18 to be exposed to the pressure in chamber 9. This leads to the hydraulic cylinder's diameter (dimension) being smaller than previously known designs. In the previously known designs exemplified in the patent application's Prior Art section, the corresponding surface 18 is omitted because the corresponding piston is permanently attached to the cylinder housing's end.

In figure 3 is shown, in a hydraulic diagram, a first application where a hydraulic cylinder 1 in accordance with the present invention is intended to be utilized. In the application the hydraulic cylinder 1 is used in a crane arm (boom) or similar. The hydraulic cylinder 1 is for example used to maneuver the crane arm's upward and downward movements. The diagram shows a hydraulic pump and accompanying tank for hydraulic oil. In the exemplifying embodiment the hydraulic cylinder 1 consists of a hydraulic cylinder of a double-acting type which is equipped with a piston rod 8 with an inner cylindrical chamber 15, in which a freely running piston 16 is moveably arranged. During pressurization of the first chamber 9 (the plus side) in the hydraulic cylinder 1, overpressure will be created in the accumulator tank and the inner chamber in the piston rod. The overpressure in the piston rod allows for the second piston 16 to move in the direction of the end 5 until it presses against the end 5. When the second piston 16 moves in into the inner chamber 15 in the piston rod 8, a compression of the fluid in the inner chamber 15 occurs. The inner chamber 15 is via at least one connection such as a hydraulic coupling or similar, connected via a hose (tubing) or similar to at least one first pressure accumulator 21. The inner chamber 15 may also via at least one connection such as a hydraulic coupling or similar, be connected via a hose (tubing) or similar to at least one second pressure accumulator 22. The pressure in pressure accumulator 21 is normally between 250-300 bar. The pressure in pressure accumulator 22 is normally between 50-80 bar. The pressure accumulator 21 may in alternative embodiments be directly connected to the hydraulic cylinder but is preferably connected to the hydraulic cylinder via at least one check valve. The hydraulic diagram also shows a control valve, a second pressure tank and other hydraulic components such as check valves. Through repeated piston strokes a pressurization of the accumulator tank is created whereby a pressurization of the inner chamber of the hydraulic piston will occur. When pressure by way of pressure spikes and the like arise in the hydraulic system, the pressure in the inner chamber 15 will cause the check valves to stop flow out from the inner chamber 15. A resisting upwardly directed force (in relation to the crane arm) will thereby be achieved via the hydraulic cylinder. If pressure in the inner chamber rises above a certain predetermined level, a flow will be allowed via a valve to a tank valve. The resisting force is dimensioned (balanced) according to the force that is necessary to hold up the crane arm. The higher pressure from pressure accumulator 21 is used during the strain of load on the crane arm. The lower pressure from pressure accumulator 22 is used when there is no or minimal load strain on the crane arm. Thanks to this design less energy will be used for maneuvering (operating) the crane.

Figure 4 shows schematically a second conceivable application for a hydraulic cylinder in accordance with the present invention. In the application the hydraulic cylinder 1 may be used in a crane or similar. In the application the hydraulic cylinder 1 may also be used in a wheel loader, dumper, excavator, back-hoe or similar. In this application at least one hydraulic cylinder is connected to a rocker arm in a vehicle or similar. In this application the hydraulic cylinder's plus side is connected via a check valve to a pressure accumulator and the inner chamber in the hydraulic piston. During movement of the hydraulic cylinder, the pumping piston's overpressure in the hydraulic cylinder's plus side will create an overpressure in the inner chamber of the piston rod. By way of the overpressure, a resisting force will be created in the hydraulic cylinder. The resisting force will lessen the energy used for maneuvering a crane arm (boom), wheel loader arm, dumper flatbed, excavator boom, back-hoe or similar. The pressure in pressure accumulator 21 is normally between 250-300 bar.

Figure 5 shows, in a hydraulic diagram, a third conceivable application for a hydraulic cylinder in accordance with the present invention. In this application the hydraulic cylinder is connected between two vehicle parts such as between the chassis and the superstructure of a vehicle. In the hydraulic diagram is shown a second cylinder 23 which is connected between the chassis and the superstructure of a vehicle or alternatively between a part of a vehicle and a counterweight or similar. During start the cylinder is pressurized by the counterweight. The counterweight creates an overpressure in the inner chamber in the hydraulic cylinder which in turn is used to lessen energy consumption when maneuvering a crane arm, boom or the like. The superstructure of a vehicle or alternatively a part of a vehicle or a counterweight pressurizes the fluid in chamber 24 in the second cylinder 23 that in turn pressurizes the fluid in chamber 15.

A fourth conceivable application for a hydraulic cylinder in accordance with the present invention is that the hydraulic cylinder can also be advantageously used for maneuvering (operating) the lifting arms and bucket of a wheel loader or similar heavy equipment. In the detailed description of the present invention, design details may have been omitted which are apparent to persons skilled in the art. Such obvious design details are included to the extent necessary so that the proper and full performance of the present invention is achieved. For example, components such as seals (washers, rings), hydraulic couplings, hydraulic hoses and several more types of components are included to the extent necessary so that the intended function is obtained.

In conceivable embodiments of the present invention, the maximum pressure in the inner cylindrical chamber 15 can be adjustable. Adjustability can be accomplished via previously know and suitable for the purpose hydraulic system circuits.

Even if certain preferred embodiments have been described in detail, variations and modifications within the scope of the invention can become apparent for specialists in the field and all such are regarded as falling within the scope of the following claims. It is conceivable that the present invention consists of a method for utilizing the present hydraulic cylinder. It is also conceivable that the present invention be defined as an energy efficient hydraulic system that includes at least one hydraulic cylinder 1 and at least one pressure accumulator in accordance with figures 3 and 4. The energy efficient hydraulic system according to the present invention may be used for operating (maneuvering) different types of equipment such as crane arms (booms) and similar and used in operating (maneuvering) heavy equipment such as wheel loader arms, excavator booms, dumper flatbeds, back-hoes and the like. Advantages of the Invention

The present invention has several advantages. The most obvious is that the hydraulic cylinder according to the present invention is substantially more energy efficient than existing types of hydraulic cylinders. The design also allows for it to be made smaller than with designs in accordance with the accounted for prior art. The design also allows for existing hydraulic cylinders to be rebuilt into a hydraulic cylinder in accordance with the present invention. The hydraulic cylinder's size can by its design be made smaller than previously known prestressed hydraulic cylinders.