COUPLING DEVICE AND A METHOD FOR COUPLING

Abstract: The invention relates to a device for positioning a coupling means in a gearbox in a first gear position, a second gear position and an intermediate neutral position, the device comprising a housing (5) which forms a working cylinder (6), a main piston (7) arranged in the working cylinder in order to interact operationally with it, a piston rod (8) which is connected rigidly to the main position and extends from a first side of the same and out of the housing, which piston rod is, outside the housing, connected to the coupling means (4), the main piston (7) being arranged displaceably between three different positions in the working cylinder, which correspond to said first and second gear positions and the neutral position, an auxiliary piston (11) which is arranged displaceably inside the housing. The auxiliary piston is adapted to interact operationally with the working cylinder and is arranged on a second, opposite side of the main piston relative to said first side.

Description: Coupling device and a method for coupling FIELD OF THE INVENTION The present invention relates to a device for positioning a coupling means in a gearbox according to the preamble of claim 1. The invention also relates to a method for positioning such a coupling means according to the preamble of claim 13. The invention will be described below in a case where the gearbox consists of what is known as a dropbox or transfer gearbox which is operationally connected to a main gearbox. Such an arrangement with a main gearbox and a transfer gearbox is found in a construction machine such as a dumper or wheel loader. The purpose of the transfer gearbox is to allow shifting between a low-gear register (low) and a high-gear register (high) and also to distribute the force between a front axle and a rear axle of the vehicle. This is a preferred but in no way limiting application of the invention. . ' Using conventional technology, shifting between low and high can be performed only when the vehicle is standing still. It is desirable for it to be possible to perform such shifting while driving so as to obtain shorter operating cycle times. PRIOR ART US 4,593,606 describes a piston/cylinder device for bringing about shifting in a gearbox. A main piston is enclosed in a first working cylinder of a housing and connected to a piston rod. The piston rod is in turn connected to a coupling means for the purpose of bringing about said shifting. A rear portion projecting from the main piston forms a second working cylinder, in which an auxiliary piston is displaceably arranged. A first pressure chamber is formed between the main piston and a first end of the first working cylinder. A second pressure chamber is formed between the mutually facing surfaces of the main piston and the auxiliary piston. A pipe for compressed air leads to the second pressure chamber through the auxiliary piston. A third pressure ' chamber is formed between the auxiliary piston and a second end of the first working cylinder. Such a piston/cylinder device is relatively complicated with two working cylinders. Furthermore, a relatively complicated control of the supply of compressed air is required in order to achieve the three positions. SUMMARY OF THE INVENTION One object of the invention is to produce a device for positioning a coupling means in a gearbox, which affords opportunities for production which,, is. more cost-effective in relation to the prior art. Another object is to produce a device which affords opportunities for rapid and reliable movement of the main piston between said positions. A further object is to produce a device which occupies a volume 1 which is smaller in relation to previously known piston/cylinder devices . The above objects are achieved by virtue of the fact that the auxiliary piston is adapted to interact operationally with the working cylinder and is arranged on a second, opposite side of the main piston relative to said first side. The expression that the piston is adapted to interact operationally with the cylinder means that the piston delimits two spaces in the working cylinder and that the piston is movable relative to the working cylinder by virtue of forces of different magnitude being applied to the opposite surfaces of the piston. In other words, the piston is arranged in such a manner in the working cylinder that a radially outer surface of the piston is located next to or at a small distance from an inner lateral surface of the working cylinder so as to be moved along the same. According to a preferred embodiment of the invention, the device comprises a first duct for pressure medium through the housing and into a space between the main piston and the auxiliary piston for moving the main piston relative to the auxiliary piston, and a second duct through the housing to a space on said first side of the main piston, the surface of the main piston accessible to the pressure medium being larger on the second side than on the first side. As a result, the main piston can, for example, be made to stop in the neutral position when shifting from low to high by virtue of the pressure medium (compressed air) being applied at the same pressure on both sides of the main piston. According to another preferred embodiment of the invention, the device comprises a regulating arrangement which in turn . comprises a pump and three valves connected to the pump, which each control air to or as the case may be from one of said first, second and third ducts. The device preferably comprises an electric control unit which is electrically connected to said valves for regulating opening or as the case may be closing of these. A further object of the invention is to provide a method for positioning a coupling means in a gearbox, which allows rapid and reliable movement of the main piston between said positions. Yet another aim is to provide a method which affords opportunities for a device for said positioning, which can be produced cost-effectively. The above objects are achieved by a method according to claim 13. Further advantageous embodiments and advantages of the invention emerge from the description below and the remaining patent claims. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in greater detail below with reference to the embodiment shown in the accompanying drawings, in which Figure 1 illustrates a cut-away cross -sectional view of a coupling means in a gearbox, which means is intended to be moved by means of the device according to the invention; Figure 2 illustrates a cross-sectional view of the device according to the invention in a preferred embodiment; Figure 3 illustrates diagrammatically a regulating arrangement included in the positioning device, and • Figure 4 illustrates a block diagram of a device for controlling the movements of the coupling means. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Figure 1 illustrates an input shaft 1 in a dropbox, or transfer gearbox, of a construction machine. The transfer gearbox is operationally connected to a main gearbox via the input shaft 1. A first and a second gear wheel 2, 3 are mounted by roller bearings on the shaft 1. A coupling means 4 is arranged in a first position, in which it is in engagement with the first gear wheel 2. This corresponds to a first gear position in the gearbox. By moving the coupling means 4 to the right in Figure 1, an intermediate neutral position is first obtained, and then a second position, in which it is in engagement with the second gear wheel 3. This second position corresponds to a second gear position in the gearbox. To be precise, the coupling means 4 consists of a coupling sleeve. The coupling sleeve 4 is connected to the shaft 1 via a spline joint and can be displaced in the axial direction by means of an arm 10 (see Figure 2) . Figure 2 illustrates a piston/cylinder device which is operationally connected to the coupling means 4 for the purpose of moving it. The device comprises a housing 5 which forms a working cylinder 6 for a main piston 7. A piston rod 8 is connected rigidly to the main piston 7 and extends from a first side 9 of the same and out of the housing 5. Outside the housing 5, the piston rod 8 is connected to the coupling means 4 (not shown) via the arm 10. To be precise, the arm 10 has a fork (not shown) which is arranged in engagement with a recess 40 in the coupling sleeve 4. The main piston 7 is arranged displaceably between three different positions in the working cylinder 6, which correspond to said first and second /gear positions and the neutral position. An auxiliary piston 11 is adapted to interact operationally with the working cylinder 6 and is arranged on a second, opposite side 12 of the main piston relative to 'said first side 9. The device comprises a first duct 13 for pressure medium through the housing and into a space 14 between the main piston 7 and the auxiliary piston 11- for moving the main piston relative to the auxiliary piston. Said first duct 13 extends through • the auxiliary piston 11 in its intended direction of movement and opens in a surface of the auxiliary piston which faces the main piston. The auxiliary piston 11 comprises a portion 15 which projects from a side of the same opposite that side of the auxiliary piston which faces the main piston 6. The projecting portion 15 comprises said first duct 13. The housing 5 comprises an opening 16, in which said projecting portion 15 is movably arranged. The movement path of the auxiliary piston 11 is limited in both a forward and a backward direction by portions 19, 20 of the housing 5. In the returned position of the auxiliary piston shown in Figure 1, a portion 21 of the auxiliary piston bears against an inner delimiting surface 19 of the working cylinder 6. The auxiliary piston has a portion 22 which projects transversely to its direction of movement and is intended, when the auxiliary cylinder is arranged in its advanced position, to bear against a portion 20 of the housing 5 projecting . into the working cylinder. The device also comprises a second duct 17 through the housing 5 to a space on said first side 9 of the main. piston 7, and a third duct 18 through the housing 5, which leads to a space on a side of the auxiliary piston 11 opposite the main piston 7. The second duct - 17 has at least in . part a smaller cross section than the third opening. The functioning of such a constriction is explained below. • The piston rod 8 is provided with three recesses 27, 28, 39. Two sensors 29, 30 are arranged for detecting the position of the piston rod by means of the recesses 27, 28, 39. Figure 3 illustrates an arrangement for regulating the supply or as the case may be the removal of pressure medium in the form of compressed air to and from the working cylinder 6 for the purpose of moving the main piston 7 between said three positions. The regulating arrangement comprises a pump 23 and three valves 24, 25, 26 connected to the pump, which each control air to or as the case may be from one of said first 13, second 17 and third 18 ducts. The valves consist of what is known as on/off valves. The shifting procedure will now be described in detail. Shifting from low to high is initiated when the vehicle has reached a predetermined speed, for example 36 km/h. The speed is sensed via a detector in a conventional manner. The application of gas to the engine and also the load (the torque) on the transfer gearbox are disconnected. The latter is brought about by the transfer gearbox being freed by brief disengagement of a coupling in the main, gearbox. The brief disengagement can extend over, for example, 0.2-0.3 seconds. The coupling means 4 is now transferred into the neutral position. This is brought about by turning on the third valve 26. Compressed air is then supplied through the third duct 18. The auxiliary piston 11 and the main piston 7 are thus moved forward together until said projecting portion 22 of the auxiliary, piston is stopped by the housing part 20. The second duct 17 has such a constriction that a sufficient quantity of air is present in the space on an -opposite side of the main piston relative to the auxiliary piston 11 in order to apply a certain counterpressure to the main piston 7. The position of the piston rod 8 is detected by means of the sensors 29, 30. When both the sensors 29, 30 sense the grooves 27, 28 in the piston rod 8, the coupling means 4 has reached the neutral position. The second valve 25 is now made to turn on. Compressed air is thus supplied through the second duct 17. By turning on the second valve 25 when the neutral position of the coupling means has been detected, the main piston can be stopped rapidly and effectively owing to the difference in area of the piston surfaces. The main piston 7 is thus made to stop in the neutral position. In order for it to be possible to bring about a rapid shifting operation, rapid synchronization of the speeds of the input shaft 1 and the output shaft (not shown) in the transfer gearbox is necessary. According to the invention, this is brought about by decelerating a retarder (torque converter) connected to the main gearbox. According to an alternative/supplementary arrangement, use is made of a multiple disk brake included in the main gearbox. According to a further alternative/supplementary arrangement, downshifting is performed in the main gearbox. The speeds of the input and output shafts are sensed and, when they at least essentially correspond to one another, the coupling means is transferred from the neutral position into engagement with the second gear wheel 3. This is brought about by turning on the first' valve 24. Compressed air is thus supplied through the . first duct 13. The main piston 7 is then moved into its end position bearing against an inner end surface of . the working cylinder 6. This is detected by the sensor 30 sensing the intermediate groove 39 in the piston rod/ 8. The torque to the transfer gearbox and the. application of gas to the engine are subsequently connected back in. ■ Shifting from high to low is initiated when the vehicle vhas- been decelerated from a higher speed to a predetermined lower speed, for example 36 km/h. The application of gas to the engine and also the load (the torque) on the transfer gearbox are disconnected in the same way as described above. The coupling means 4 is moved into the neutral position by virtue of the main piston 7 being moved into its intermediate position. The latter is brought about by turning on the second valve 25. Compressed air is then supplied to the second duct 17. The still pressurized auxiliary piston 11 stops the movement of the main piston 7 in the neutral position. The neutral position is detected by the sensors 29, 30 sensing the grooves 27, 28. Synchronization of the speeds of the input shaft 1 and the output shaft (not shown) in the transfer gearbox is effected by accelerating the input shaft. This is brought about via electronic injection of fuel into the engine. As an alternative or supplementary arrangement, upshifting is performed in the main gearbox. The speeds of the input and output shafts are sensed and, when they at least essentially correspond to one another, the coupling means 4 is transferred from the neutral position into engagement with the first gear wheel 2. This is brought about by turning off the third valve 26. The main piston 7 is then moved into its other end position. This is detected by the sensor 29 sensing the intermediate groove 39 in the piston rod 8. The torque to the transfer gearbox and the application of gas to the engine are subsequently connected back in. The table below indicates the positions of the valves 24, 25, 26 and the sensors 29, 30 in low gear, neutral position and high gear. In high gear, the solenoid valve 26 can also be turned on (1) . a Figure 4 illustrates in a block diagram a device for controlling the movements of the coupling means according to the shifting operations described above. An electric control unit 31 is coupled to the sensors 29, 30, the solenoid valves 24, 25, 26, a detector 32 • for sensing the speed of the vehicle, a valve 33 for •• disconnecting the accelerator of the vehicle, said coupling 34 in the main gearbox, the retarder 35, an : arrangement 36 for regulating the fuel supply to the engine, and detectors 37, 38 for sensing the speed of the input shaft 1 and output shaft. The wording that the movement path of the auxiliary piston is limited in both a forward and a backward direction by portions of the housing means that said housing portions also include parts connected to the housing. The neutral position referred to above can comprise a number of positions. The invention is not to be considered as being limited to the illustrative embodiments described above, but a number of further variants and modifications are possible within the scope of the patent claims below.

Claims: PATENT CLAIMS 1. A device for positioning a coupling means (4) in a gearbox in a first gear position, a second gear position and an intermediate neutral position, the device comprising a housing (5) which forms a working cylinder (6) , a main piston (7) arranged in the working cylinder in order to interact operationally with it, a piston rod (8) which is connected rigidly to the main piston and extends from a first side (9) of the same and out of the housing, which piston rod is, outside the housing, connected to the coupling means. (4), the main piston (7) being arranged displaceably between three different positions in the working cylinder, which correspond to said first and second gear positions and the neutral position, an auxiliary piston (11)- which is arranged displaceably inside the housing, characterized in that the auxiliary piston .(11) is adapted to interact operationally with the working cylinder (6) and is arranged on a second, opposite side (12) of the main piston (7) relative to said first side (9). 2. The device as claimed in claim 1, characterized in that the device comprises a first duct (13) for pressure medium through the housing and into a space between the main piston (7) and the auxiliary piston (11) for moving the main piston relative to the auxiliary piston. 3. The device as claimed in claim 2, characterized in that the device comprises a second duct (17) through the housing to a space on said first side (9) of the main piston (7) , and in that the surface of the main piston accessible to the pressure medium is larger on the second side (12) than on the first side (9) . 4. The device as claimed in any one of the preceding claims, characterized in that the device comprises a third duct (18) for pressure medium through the housing, which leads to a space on a side of the auxiliary piston opposite the main piston. 5. The device as claimed in any one of the preceding claims, characterized in that the device comprises, an arrangement for regulating the supply or as the case may be the removal of pressure, medium in the form of compressed air to and from the working cylinder (6) .for the purpose of moving the main piston (7) between said three positions. 6. The device as claimed in claims 3, 4 and 5, characterized in that the regulating arrangement comprises a pump (23) and three valves (24, 25, ,26) connected to the pump, which each control air to o as the case may be from one of said first, second and third ducts (13, 17, 18). • 7. ■ The device as claimed in claim 6, characterized in that said valves (24, 25, 26) consist of solenoid valves . 8. The device as claimed in claim 6 or 7, characterized in that the device comprises an electric control unit (31) which is electrically connected to said valves (24, 25, 26) for regulating opening or as the case may be closing of these. 9. The device as claimed in claim 8, characterized in that the device comprises at least one sensor (29, 30) connected to the electric control unit (31) for detecting the position of the coupling means (4) . 10. The device as claimed in any one of the preceding claims, characterized in that the movement path of the auxiliary piston (11) is limited in both a forward and a backward direction by portions (19, 20) of the housing. 11. The device as claimed in any one of the preceding claims, characterized in that said gearbox is a transfer gearbox which is operationally connected to a main gearbox. 12. The device as claimed in any one of the preceding. claims, characterized in that the device is intended for a construction machine such as a dumper or a wheel loader. 13. A method for shifting between a first gear position, a second gear position and an intermediate .neutral position in a gearbox, the shifting being brought about by moving a coupling means (4) from. a first position, . in which it is in engagement, with■ • - a first gear wheel (2), into the neutral position and on into a second position, in which it is in engagement with a second gear wheel (3) , which first and second gear wheels are mounted on an input shaft (1) of the gearbox, the input shaft is disengaged from load from an engine coupled to it, after which the coupling means (4) is moved from the first position into the neutral position and on into the second position, characterized in that the speeds of the second gear wheel (3) and. said shaft are controlled to essentially the same valu before the coupling means (4) is moved from the neutral position into the second position. 14. The method as claimed in claim 13, characterized in that, on upshifting, said speed control is effected by decelerating the input shaft (1) by means of a brake connected thereto. 15. The method as claimed in claim 14, characterized in that said brake consists of a retarder. 16. The method as claimed in claim 14, characterized in that said brake consists of a multiple disk brake in a main gearbox connected to said gearbox. 17. The method as claimed in any one of claims 13-16, characterized in that, on upshifting, said speed control is effected by downshifting in a main gearbox connected to said gearbox. 18. The method as claimed in any one of claims 13-17, characterized in that a main piston (7) in a piston/cylinder device, which piston is operationally connected to the coupling means (4) , is brought into an intermediate position for bringing about the neutral position. 19. The method as claimed in claim 18, characterized in that the position of - the coupling means (4) is detected and the main piston (7) is made to stop in the neutral position until the speed adaptation has been effected. 20. The method as claimed in claim 18 or 19, characterized in that, when the presence of the coupling means (4) in the neutral position has been detected, the main piston (7) is made to stop in the intermediate position by application of a counterpressure to it. 21. The method as claimed in any one of claims 13-20, characterized in that a speed of an output shaft from the gearbox or of a rotation means coupled to the output shaft is measured, in that the load to the input shaft (1) of the gearbox is disengaged at a predetermined speed, and in that the abovementioned shifting operation is subsequently performed. 22. The method as claimed in any one of claims 13-21, characterized in that the gearbox consists of a transfer gearbox which is operationally connected to a main gearbox, and in that the disengagement of said input shaft (1) is effected by virtue of an output shaft of the main gearbox being disengaged.

Inventors: ERIKSSON KARIN, JOHANSSON HAAKAN, KNECHT EMIL, MOHLIN JOHAN, ERIKSSON, KARIN, JOHANSSON, HAAKAN, KNECHT, EMIL, MOHLIN, JOHAN
Applicants: ERIKSSON KARIN, JOHANSSON HAOKAN, KNECHT EMIL, MOHLIN JOHAN, VOLVO CONSTR EQUIP COMPONENTS, ERIKSSON, KARIN, JOHANSSON, HAAKAN, KNECHT, EMIL, MOHLIN, JOHAN, VOLVO CONSTRUCTION EQUIPMENT COMPONENTS AB
Application year: 2001
Main classification: F16H3
IPC codes: F16H61, F16H63