CYLINDER, HYDRAULIC SYSTEM, CONSTRUCTION MACHINE AND PROCEDURE

Abstract

A cylinder has a piston part, a cylinder part, and a pipe section connected to the piston or cylinder parts. A portion of the pipe section encloses a pressure compartment which receives a fluid to apply a pressure on a pressure surface so the piston part is displaced in a first stroke direction. A first return pressure compartment receives a fluid to apply a pressure on a first return pressure surface so that the piston part is displaced in a second return stroke direction. The first return pressure compartment is positioned on the outside of the pipe section, and the area of the first return pressure surface is substantially equal to the area of the return pressure surface so that a volume-neutral operation of the cylinder is provided. Also described is a hydraulic system, an excavator comprising the cylinder and a procedure for operation of the cylinder.

Claims

1.-23. (canceled)

24. A cylinder comprising: a piston part; a cylinder part arranged for axial movement relative to the piston part, the piston part and/or the cylinder part comprising a pipe section; one or more pressure compartments arranged to receive a fluid to apply a pressure on one or more pressure surfaces for displacement of the piston part in a first stroke direction, wherein a portion of the pipe section encloses the or at least one of said pressure compartments and/or pressure surfaces in a radial inner region of the cylinder; and return pressure compartments arranged to receive a fluid to apply a pressure on return pressure surfaces for displacement of the piston part in a second stroke direction, the return pressure compartments comprising at least one first return pressure compartment and at least one second re-turn pressure compartment, wherein the at least one first return pressure compartment and/or at least one first return pressure surface is defined in a radial outer region of the cylinder; wherein the pipe section further encloses said at least one second return pressure compartment and/or at least one second return pressure surface; and wherein the pipe section permits fluid communication between the first return pressure compartment and the second return pressure compartment.

25. The cylinder according to claim 24, wherein the pipe section comprises at least one port arranged to provide fluid communication between the first return pressure compartment and the second return pressure compartment.

26. The cylinder according to claim 24, configured for volume-neutral or approximately volume-neutral operation.

27. The cylinder according to claim 24, wherein the return pressure surfaces have together in total an area which is equal to or approximately equal to the total area of the pressure surface(s).

28. The cylinder according to claim 24, wherein the return pressure surfaces have in total an area size projected onto a plane perpendicular to the stroke direction which is equal to or approximately equal to the pressure surface's area size project-ed onto a plane perpendicular to the stroke direction.

29. The cylinder according to claim 24, wherein the at least one first return pressure compartment and/or return pressure surfaces in the radial outer area of the cylinder is positioned on the outside of the pipe section.

30. The cylinder according to claim 24, wherein the cylinder part or the piston part has a first end which comprises a guide for the other of the cylinder part and the piston part and an opposite, second end which is closed for the other of the cylinder part and the piston part.

31. The cylinder according to claim 24, further comprising at least one third return pressure compartment and/or at least one third return pressure surface.

32. The cylinder according to claim 31, further comprising a cylinder pipe between the first return pressure compartment and the third return pressure compartment, and the cylinder pipe comprises at least one port arranged to provide fluid communication between the first return pressure compartment and the third return pressure compartment.

33. The cylinder according to claim 32, wherein the third return pressure compartment is defined in the radial outer region of the cylinder, and the second return fluid compartment is in fluid communication with the third return fluid compartment.

34. A cylinder comprising: a piston part; a cylinder part which in a first end comprises a guide for the piston part and which in an opposite, second end is closed for the piston part; one or more pressure compartments arranged to receive a fluid to apply a pressure on one or more pressure surfaces for displacement of the piston part in a first stroke direction; and return pressure compartments arranged to receive a fluid to apply a pressure on return pressure surfaces for displacement of the piston part in a second return stroke direction, the return pressure compartments comprising at least one first return pressure compartment and at least one second return pressure compartment arranged in fluid communication through a pipe section of the cylinder part or the piston part; the pressure compartments and the return pressure compartments being configured for volume-neutral or approximately volume-neutral operation of the cylinder.

35. A cylinder comprising: a piston part; a cylinder part arranged for axial movement relative to the piston part; one or more pressure compartments arranged to receive a fluid to apply a pressure on one or more pressure surfaces for displacement of the piston part in a first stroke direction; and return pressure compartments arranged to receive a fluid to apply a pressure on return pressure surfaces for displacement of the piston part in a second stroke direction; a pipe section which is connected to the piston part or the cylinder part, wherein a portion of the pipe section encloses the or at least one of said pressure compartments which in an axial direction is delimited by the or at least one of said pressure surfaces; the return pressure compartments comprising at least one first return pressure compartment and at least one second return pressure compartment arranged in fluid communication, at least said first return pressure compartments and/or the return pressure surfaces being positioned on the outside of the pipe section.

36. A hydraulic system comprising a hydraulic circuit which comprises at least one cylinder according to claim 35.

37. The hydraulic system according to claim 36, wherein the hydraulic circuit is closed.

38. The hydraulic system according to claim 37, wherein the closed circuit comprises a top-up pump and an oil tank arranged to supply top-up oil to the closed circuit.

39. The hydraulic system according to claim 38, wherein the oil tank is arranged to supply the top-up oil to the circuit through at least one check valve.

40. The hydraulic system according to claim 36, wherein the cylinder is connected to a fluid pump configured to being driven with a rotation direction which is switchable between a first rotation direction and a second rotation direction, wherein in the first rotation direction the pump operates to supply fluid to the cylinder's pressure compartment, and in the second rotation direction the pump operates to supply fluid to the cylinder's return pressure compartment.

41. The hydraulic system according to claim 40, wherein the fluid pump is connected to an electric motor, and the electric motor is connected to a frequency converter arranged to change the rotation direction and the RPM of the electric motor and/or the pump.

42. A construction machine comprising at least one cylinder according to claim 35.

43. A construction machine comprising a hydraulic system according to claim 36.

44. A method of operating a cylinder according to claim 36, wherein the procedure comprises the step of pumping a fluid to the cylinder.

45. The method according to claim 44, wherein the cylinder is connected to a fluid motor which is connected to an electric motor which is connected to a frequency converter; and the procedure further comprises the step of giving a control signal to the frequency converter so that the electric motor and the pump rotate in a desired direction and at a de-sired speed to thereby guide the fluid from the pump to the cylinder.

46. The method according to claim 45, wherein the procedure further comprises the step of generating electric energy by allowing the cylinder to, when loaded, guide fluid into the pump so that the electric motor which is connected to the pump is subjected to a rotation, and thereby generate energy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Hereunder are described examples of embodiments with reference to the attached drawings, wherein:

[0075] FIG. 1a shows a simplified principle drawing of a first embodiment of a volume-neutral cylinder;

[0076] FIG. 1b shows a simplified principle drawing of the cylinder part belonging to the cylinder in FIG. 1a;

[0077] FIG. 1c shows a simplified principle drawing of the piston part belonging to the cylinder in FIG. 1a;

[0078] FIG. 1d shows a detailed axial section of the cylinder in FIG. 1a;

[0079] FIG. 1e shows a radial section of the cylinder in FIG. 1d;

[0080] FIG. 2a shows a simplified principle drawing of a second embodiment of a volume-neutral cylinder;

[0081] FIG. 2b shows a simplified principle drawing of the cylinder part belonging to the cylinder in FIG. 2a;

[0082] FIG. 2c shows a simplified principle drawing of the piston part belonging to the cylinder in FIG. 2a;

[0083] FIG. 2d shows a detailed axial section of the cylinder in FIG. 2a;

[0084] FIG. 2e shows a radial section of the cylinder in FIG. 2a;

[0085] FIG. 3a shows a simplified principle drawing of a third embodiment of a volume-neutral cylinder;

[0086] FIG. 3b shows a simplified principle drawing of the cylinder part belonging to the cylinder in FIG. 3a;

[0087] FIG. 3c shows a simplified principle drawing of the piston part belonging to the cylinder in FIG. 3a;

[0088] FIG. 3d shows a detailed axial section of the cylinder in FIG. 3a;

[0089] FIG. 3e shows a radial section of the cylinder in FIG. 3a;

[0090] FIG. 4a shows a top sketch of an excavator with an electro-hydraulic system comprising a volume-neutral cylinder;

[0091] FIG. 4b shows the excavator of FIG. 4a in a perspective view;

[0092] FIG. 5 shows a schematic diagram for an electro-hydraulic system comprising a volume-neutral cylinder; and

[0093] FIG. 6 shows the electro-hydraulic system comprising a double acting cylinder according to prior art.

DETAILED DESCRIPTION OF THE DRAWINGS

[0094] In the figures, the same reference is used for elements with identical technical function. Attention is drawn to the fact that the FIGS. 1a-c, 2a-c and 3a-c are simplified principle drawings, and that details may have been left out on these and other figures to better emphasise the invention itself and its principle of operation.

[0095] In the FIGS. 1a-3e, three embodiments 1A, 1B, 1C are described for a cylinder according to the first aspect of the invention, wherein the cylinder 1A, 1B, 1C comprises a cylinder part and a piston part and is configured in a volume-neutral manner, which is known as volume-neutral cylinder in technical terminology.

[0096] A volume-neutral cylinder can be distinguished in that the total area of all pressure surfaces TF is identical to the total area of all opposing return pressure surfaces RTF. This applies if all the pressure surfaces and the return pressure surfaces in their entirety are located in parallel planes perpendicular to the axial movement of direction of the cylinder part relative to the piston part. Thereby, when the pressure compartment TR is supplied with a given amount of fluid through a pressure port 235, a corresponding amount of fluid can be drained through a return port 335, vice versa, so that the piston part 300 can be displaced an equal distance in a stroke direction A as in a stroke direction B, regardless of whether the given amount of fluid is supplied to the pressure compartment TR or a return pressure compartment RTR. The fluid can be oil.

[0097] All three cylinders 1A, 1B, 1C comprise a cylinder part 200 and a piston part 300 which are axially mutually displaceable relative to each other. The piston part 200 is not through. Thereby the cylinders can be end mounted 1A, 1B, 1C. End mounting can be understood as the cylinder part 200 and the piston part 300 being mountable in their respective ends, so that the distance between the cylinder fittings and the total length of the cylinder can be regulated by displacing the piston part 200 relative to the cylinder part 300.

[0098] Reference is made firstly to the first embodiment 1A, wherein the FIGS. 1a, 1b and 1c show simplified principle drawings of the cylinder 1A, the cylinder part 200 and the piston part 300. FIG. 1d shows a detailed axial section of the cylinder 1A and FIG. 1e shows a radial section A-A of the cylinder 1A.

[0099] The cylinder 1A comprises a piston part 300, a cylinder part 200 which on one end comprises a guide 230 for the piston part 300, and which on an opposite second end comprises a cylinder fitting 230. A pipe section 400 is connected to the cylinder part 200, wherein a portion of the pipe section 400 encloses a pressure compartment TR which in an axial direction is delimited by at least one pressure surface TF. The pressure compartment TR is arranged to receive a fluid for applying a pressure on the at least one pressure surface TF so that the piston part 300 is displaced in the first stroke direction A.

[0100] A first return pressure compartment RTR1 arranged to receive a fluid for applying a pressure on at least one first return pressure surface RTF1 so that the piston part 300 is displaced in the second return stroke direction B. The first return pressure compartment RTR1 is positioned on the outside of the pipe section 400 and is annular. The area of the at least one first return pressure surface RTF1 is identical to the area of the at least one return pressure surface TF so that a volume-neutral operation of the cylinder is provided.

[0101] In FIG. 1d, the pressure surface TF is shown centred and distributed between several planes formed by a piston rod 310, a locking element 341 and a piston 340.

[0102] The cylinder 1A further comprises a plurality of cavities 99, which in FIGS. 1a and 1d are closed, so that the air pressure in the cavities 99 changes with the position of the piston part. In an embodiment that is not shown, the cavities 99 can be ventilated so that the pressure in the cavities 99 is the same as the atmospheric pressure.

[0103] A rear coupling element 230 connects the pipe section 400 and an outer cylinder house 210. The rear coupling element 230 can comprise the pressure port 235 and a bolt hole 233, as shown in the FIGS. 1a-1d. Said elements are shown connected by a plurality of screws. In an alternative embodiment (not shown), two or more of the said elements can be connected to each other by a thread connection.

[0104] Further, the cylinder part 200 comprises a cylinder piston 241 which is fixed to the pipe section 400 and which forms an interior guide for the piston rod 310. A return port 335 is positioned in the outer cylinder house 210.

[0105] A front connection portion 330 connects the piston rod 310 and the piston pipe 320. On the end of the piston rod, a piston 340 with an associated locking element 341 is mounted. A first ring piston 342 is connected to the piston pipe 320 and abuts in a guiding manner the inside of the outer cylinder house 210 and the outside of the pipe section 400.

[0106] Reference is then made to the second embodiment 2B, wherein the FIGS. 2a, 2b and 2c show simplified principle drawings of the cylinder 2B and the cylinder part 200 and the piston part 300. FIG. 2e shows a detailed axial section of the cylinder and FIG. 2e shows a radial section B-B of the cylinder.

[0107] In the second embodiment 1B, the pipe section 400 is connected to the piston part 300. The pipe section 400 functionally replaces the piston rod 330 in the first and the third embodiment 1A, 1C.

[0108] The pressure compartment TR and the associated pressure surface TF are positioned in the piston part's first end 300A.

[0109] The first return pressure compartment RTR1 is supplied with a second return pressure compartment TRF2 and a second return pressure surface TRF2 positioned on the inside of the pipe section 400 and on the outside of a cylinder pipe 240 associated with the cylinder part. The cylinder pipe 240 comprises an axial fluid channel 236.

[0110] When the piston part 300 is to be guided in the first stroke direction A, the fluid is supplied via the pressure port 235 and the fluid channel 236 so that a fluid pressure is provided on the pressure surface TF. When the piston part 300 is to be guided in the second stroke direction B, the fluid is supplied through the return pressure port 335. The pipe section 400 comprises at least one port 333 so that the fluid being led in and out through the return pressure port 335 can flow between the first return pressure compartment RTR1 and the second return pressure compartment RTR2. Thereby an identical fluid pressure can be provided in the first return pressure compartment RTR1 and the second return pressure compartment RTR2.

[0111] The area of the first return pressure surface RTF1 and the second return pressure surface RTF2 is identical to the area of the pressure surface TF.

[0112] Reference is then made to the third embodiment 3B, wherein the FIGS. 3a, 3b and 3c show simplified principle drawings of the cylinder 3B and the cylinder part 200 and the piston part 300. FIG. 3e shows a detailed axial section of the cylinder and FIG. 3e shows a radial section C-C of the cylinder.

[0113] In the third embodiment 1C, the pipe section 400 is connected to the cylinder part 200, corresponding to the first embodiment 1A. The first return pressure compartment RTR1 and the second return pressure compartment RTR2 is supplied with a third return pressure compartment RTR3 with a third return pressure surface TRF3. The third return pressure compartment RTR3 is positioned on the outside of the pipe section 400 and on the inside of a piston pipe 320 which is positioned between the pipe section 400 and the cylinder pipe 210. The piston pipe 320 belongs to the piston part 300. The piston pipe 320 and the pipe section 400 comprise a plurality of ports 333 so that the fluid can flow between the first return pressure compartment RTR1, the second return pressure compartment RTR2 and the third return pressure compartment RTR3. Thereby an identical fluid pressure can be provided in the first return pressure compartment RTR1, the second return pressure compartment RTR2 and the third return pressure compartment.

[0114] The area of the first return pressure surface RTF1, the second return pressure surface RTF2 and the third return pressure surface RTF2 is identical to the area of the pressure surface TF.

[0115] The pressure areas and return pressure areas can be calculated. For the third embodiment 1C, for example the below formula may be used, wherein A2 is the area of the pressure surface TF and A1, A3 and A4 are the areas of the return pressure surfaces RTF1, RTF2 and RTF3.

A2=Al+A3−A4

A1=3.14/4(D2−D1.sup.2)

A2=3.14/4(D2.sup.2)

A3=3.14/4(D6.sup.2−D3.sup.2)

A4=3.14/4(D5.sup.2−D4.sup.2)

[0116] The volume-neutral cylinder 1A, 1B, 1C described herein substantially provides the same build-in measurements and stroke as a regular double acting cylinder with end mounting, because the cylinder does not have a through piston rod. The volume-neutral configuration is different from a volume-neutral cylinder according to prior art by the pressure compartment TR being centred and the corresponding return pressure compartment RTR being partially or fully arranged radially externally to the pressure compartment TR. This facilitates use of volume-neutral cylinders where end mounting is required and where there is limited space.

[0117] In an alternative embodiment which is not shown, the cylinder part 200 may have side attachment wherein two radially opposing cylinder fittings are arranged on the radial surface of the cylinder pipe. Such an attachment is known to be used on tipping cylinders for lorries and trailers.

[0118] In a further embodiment which is not shown, the cylinder part can be fastened to a foundation so that the cylinder part 200 provides a fixed position for the foundation.

[0119] The FIGS. 4a and 4b show an excavator 90 comprising an electro-hydraulic system 99 according to the second aspect of the invention and three volume-neutral cylinders 1B on the FIGS. 4a and 4b indicated by the reference numbers 6, 7 and 8. The cylinders 8, 6, 7 are end mounted, as is common on excavators.

[0120] The excavator 90 comprises a transportation device 11 with belts for movement of the excavator 90. On top of the transportation device 11, a frame construction 35 is arranged rotatably about an axis 36. On the frame construction 35, batteries 10 and fittings 40 are mounted for fitting of a digging boom 5. A boom cylinder 8 operates the digging boom 5. A stick cylinder 6 operates a dipper stick 9, and a bucket cylinder 7 operates a digging bucket 15.

[0121] Additionally, on the frame construction 35, a number of electro-hydraulic aggregates 12 are mounted, each with an electric motor 16, a pump 18 and a frequency converter 13. In addition, the electro-hydraulic system 99 comprises an oil tank 17 and a swivelling motor 3 which provides rotation about the axis 36.

[0122] An operator cab 4 contains operation handles 25 with a control unit 24 for operation of cylinder functions for the cylinders 6, 7 and 8.

[0123] To minimise the energy loss between the battery 10 and work performed with a digging bucket 15, the oil flow 30 to each of the cylinders 6, 7 and 8 is operated by individual pumps 18 driven by electric motors 16 which are RPM regulated by frequency converters 13 connected to the battery 10 through the connection 19.

[0124] FIG. 5 shows a schematic diagram for the electro-hydraulic system 99 in the FIGS. 4a and 4b. The cylinder 1b in FIG. 5 corresponds to one of the cylinders 6, 7, 8 in the FIGS. 4a and 4b.

[0125] The electric motor 16 drives the hydraulic pump 18 which generates a hydraulic pressure and an oil flow for activation of the cylinder 3B. A frequency converter 13 regulates the RPM and rotation direction of the electric motor 16. Thereby the stroke direction of the cylinder 1b can be regulated directly from the electric motor 16 without the use of directional control valves.

[0126] Because the cylinder 1B is volume neutral, the oil flow in the cylinder's pressure compartment TR and the return pressure compartment RTR (see FIGS. 3a and 3d) is identical. When the digging boom 5 in FIGS. 4a and 4b is to be raised, an oil flow and an oil pressure is supplied to the pressure compartment TR, and the piston part 300 is displaced out of the cylinder house 200.

[0127] When the digging boom 5 is lowered, energy can be regenerated by fluid flowing through the pump 18 so that it functions as a motor. As the pump 18 is connected to the electric motor 16, the electric motor 16 will function as a generator which generates energy to the battery 10 through the frequency converter 13. A corresponding regeneration can occur for the stick cylinder 6 and the bucket cylinder 7.

[0128] The electro-hydraulic system 99 further comprises a separate circuit for top-up of oil due to any internal leaks in the hydraulic circuit. Top-up is done by a pump 54 connected to a tank 17 leading oil to the pressure side TS and the return side TR through a check valve 55. The check valve shown in FIG. 5 is dual, so that the oil can be supplied to both the pressure side TS and the return side TR.

[0129] FIG. 6 shows an alternative hydraulic system 96, wherein the volume-neutral cylinder 1B is replaced with another double-acting cylinder 6a which is not volume neutral. Because the cylinder 6a has a different area on the pressure side TS than the return side TR, a different amount of oil will be supplied and drained when the piston part 300 is lead out of or into the cylinder house 200.

[0130] In FIG. 6, the electric motor 16 rotates in only one direction, and the stroke direction of the cylinder 6a is therefore regulated with a directional control valve 14, controlled by a PLS 21, assigned to the control unit 24 and the operation handle 25. Further, two counterbalance valves 27, 28 are shown.

[0131] It should be noted that all embodiments mentioned above illustrate the invention, but do not delimit it, and experts on the area will be able to design many alternative embodiments without deviating from the scope of the attached claims. In the claims, the reference numbers in parenthesis shall not be considered delimiting.

[0132] The use of the verb “to comprise” and its different forms does not exclude the presence of elements or steps not mentioned in the claims. The indefinite articles “a” or “an” before an element do not exclude the presence of more such elements.

[0133] The fact that some features are specified in mutually different dependent claims does not indicate that a combination of these features cannot be used advantageously.