COUPLING DEVICE AND A METHOD FOR COUPLING

Abstract

Method and apparatus for positioning a coupling means in a gearbox in a first gear position, a second gear position and an intermediate neutral position. The apparatus includes a housing (5) that forms a working cylinder (6), a main piston (7) arranged in the working cylinder (6) in order to interact operationally therewith, and a piston rod (8) connected rigidly to the main piston and extending from a first side thereof out of the housing (5). The piston rod (8) is connected to the coupling means or mechanism (4) outside the housing. The main piston (7) is arranged displaceably between three different positions in the working cylinder that correspond to the first and second gear positions, and the neutral position. An auxiliary piston (11) is also arranged displaceably inside the housing. The auxiliary piston (11) is adapted to operationally interact with the working cylinder and is arranged on a second, opposite side of the main piston relative to the first side.

Description

BACKGROUND OF INVENTION

[0002] 1. Field of the Invention

[0003] The present 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 invention also relates to a method for such positioning of a coupling means in a gearbox.

[0004] The invention is described hereinbelow configured so that the gearbox includes a dropbox or transfer gearbox that 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. It should be appreciated, however, that this is a preferred, but in no way limiting, application of the invention.

[0005] 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 (traveling) and thereby obtaining shorter operating cycle times.

[0006] 2. Background Art

[0007] U.S. Pat. No. 4,593,606 describes a piston/cylinder device for bringing about shifting action 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 such 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 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.

[0008] Devices that are equipped with such a piston/cylinder device are 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 INVENTION

[0009] One object of the invention is to produce a device for positioning a coupling means in a gearbox that affords opportunities for manufacture that are more cost-effective in relation to the prior art. Another object is to produce a device that affords opportunities for rapid and reliable movement of the main piston between the several positions. A further object is to produce a device that occupies a smaller space in relation to previously known piston/cylinder devices.

[0010] The above objects are achieved, at least in part, 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 radial 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.

[0011] According to a preferred embodiment of the invention, the device includes 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. A second duct is provided through the housing to a space on the first side of the main piston. The surface of the main piston is accessible to the pressure medium and is 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.

[0012] According to another preferred embodiment of the invention, the device includes a regulating arrangement that includes a pump and three valves connected to the pump and which each control air to, or as the case may be, from one of said first, second and third ducts. The device preferably comprises (includes) an electric control unit that is electrically connected to the valves for regulating opening, or as the case may be, closing of the valves.

[0013] A further object of the invention is to provide a method for positioning a coupling means in a gearbox that allows rapid and reliable movement of the main piston between the different positions. Yet another aim is to provide a method that affords opportunities for a device for this positioning which can be cost-effectively produced.

[0014] Further advantageous embodiments and advantages of the invention emerge from the description below and the associated patent claims.

BRIEF DESCRIPTION OF DRAWINGS

[0015] The invention will be described in greater detail below with reference to the embodiment shown in the accompanying drawings, in which:

[0016] FIG. 1 is a cut-away cross-sectional view of a coupling means in a gearbox that is intended to be moved by means of a device configured according to the present invention;

[0017] FIG. 2 is a cross-sectional view of a controlled device configured according to a preferred embodiment of the present invention;

[0018] FIG. 3 is a diagram illustrating a regulating arrangement included in the positioning device; and

[0019] FIG. 4 is a schematic block diagram demonstrating a device for controlling the movements of an exemplary coupling means.

DETAILED DESCRIPTION

[0020] FIG. 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 gearwheel 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 FIG. 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 is obtained. This second position corresponds to a second gear position in the gearbox.

[0021] In this exemplary embodiment, the coupling means 4 takes the form of a slidable coupling sleeve 4. 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 as depicted in FIG. 2.

[0022] FIG. 2 illustrates a piston/cylinder device that is operationally connected to the coupling means 4 for the purpose of moving it. The device comprises (includes) a housing 5 that 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 piston 7 and out of the housing 5. Outside the housing 5, the piston rod 8 is connected to the coupling-means 4 via the arm 10. Exemplarily, the arm 10 can have a fork that is arranged in engagement with a recess 40 in the coupling sleeve 4.

[0023] The main piston 7 is arranged displaceably between three different positions in the working cylinder 6 that correspond to first, second and neutral gear positions. 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 a first side 9.

[0024] 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. The first duct 13 extends through the auxiliary piston 11 in its intended direction of movement and opens in a surface of the auxiliary piston that faces the main piston.

[0025] The auxiliary piston 11 comprises a portion 15 which projects from a side of that same opposite side of the auxiliary piston which faces the main piston 6. The projecting portion 15 comprises the first duct 13. The housing 5 comprises an opening 16, in which the 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 FIG. 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.

[0026] The device also includes a second duct 17 passing through the housing 5 to a space on the first side 9 of the main piston 7. A third duct 18 is provided through the housing 5 and 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.

[0027] 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.

[0028] FIG. 3 illustrates an arrangement for regulating the supply, or as the case may be, the removal of pressure medium, exemplarily in the form of compressed air, to and from the working cylinder 6 for the purpose of moving the main piston 7 between the three positions. The regulating arrangement comprises a pump 23 and three valves 24 that each control air to (or from) the first 13, second 17 and third 18 ducts, respectively. The valves establish what are commonly known as on/off valves.

[0029] 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 supply of gas to the engine, as well as the load (torque) on the transfer gearbox, is 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.

[0030] 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 the 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 counter-pressure to the main piston 7.

[0031] 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 difference in area of the piston surfaces. The main piston 7 is thus made to stop in the neutral position.

[0032] 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 or supplementary arrangement, use is made of a multiple disk brake included in the main gearbox. According to a further alternative or supplementary arrangement, downshifting is performed in the main gearbox.

[0033] 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 the turning on of the first valve 24 causing compressed air to be 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.

[0034] Shifting from high to low is initiated when the vehicle has been decelerated from a higher speed to a predetermined lower speed, for example 36 km/h. The application of gas to the engine and load (the torque) upon 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.

[0035] 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.

[0036] The speeds of the input and output shafts are sensed and, when they at least essentially or substantially 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.

[0037] 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.

[t1]
	Low	Neutral
	gear	position	High gear
Solenoid valve low gear (25)	1	0	0
Solenoid valve neutral position (26)	0	1	0
Solenoid valve high gear (24)	0	0	1
Sensor high gear (30)	0	1	1
Sensor low gear (29)	1	1	0

[0038] In high gear, the solenoid valve 26 can also be turned on (1).

[0039] FIG. 4 illustrates, via a block diagram, a device for controlling the movements of the coupling means or mechanism 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, the 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.

[0040] It should be understood that the movement path of the auxiliary piston is limited in both a forward and a backward direction by portions of the housing, typically in the form of parts that are connected to the housing.

[0041] The neutral position referred to above can comprise a number of positions.

[0042] The invention is not to be considered as being limited to the illustrative embodiment(s) described herein, but a number of further variants and modifications are possible within the scope of the patent claims below.

Claims

1. A device for positioning a coupling mechanism in a gearbox in a first gear position, a second gear position and an intermediate neutral position, the device comprising a housing which forms a working cylinder; a main piston arranged in the working cylinder for reciprocating operation therein; a piston rod rigidly connected to the main piston and extending from a first side of the main piston out of the housing where the piston rod is connected to a coupling mechanism, the main piston being arranged displaceably between three different positions in the working cylinder and which correspond to first and second gear positions, and a neutral position; an auxiliary piston displaceably arranged inside the housing and being adapted to operationally interact with the working cylinder, the auxiliary piston being arranged on a second side of the main piston opposite to the first side thereof; and sensors adapted for detecting the position of the coupling mechanism.

2. The device as recited in claim 1, further comprising a first duct configured to conduct 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.

3. The device as recited in claim 2, further comprising a second duct configured to conduct pressure medium through the housing to a space on said first side of the main piston, and a surface of the main piston that is exposed to the pressure medium is larger on the second side than on the first side.

4. The device as recited in claim 1, further comprising a third duct configured to conduct pressure medium through the housing to a side of the auxiliary piston opposite the main piston.

5. The device as recited in claim 1, further comprising a regulating arrangement for regulating the supply of compressed air to and from the working cylinder for the purpose of moving the main piston between the three positions.

6. The device recited in claim 5, wherein the regulating arrangement further comprises a pump and three valves connected to the pump, and each of the three valves configured to control air supplied to at least one of the first, second and third ducts.

7. The device as recited in claim 6, wherein the valves are solenoid-type valves.

8. The device as recited in claim 6, further comprising an electric control unit that is electrically connected to the valves and configured for regulating opening and closing of the valves.

9. The device as recited in claim 8, further comprising at least one sensor connected to the electric control unit for detecting the position of the coupling means.

10. The device as recited in claim 1, wherein the movement path of the auxiliary piston is limited in both a forward and a backward direction by portions of the housing.

11. The device as recited in claim 1, wherein the gearbox is a transfer gearbox that is operationally connected to a main gearbox.

12. The device as recited in claim 1, wherein the device is intended for a construction machine of a type including dumpers and wheel loaders.

13. A method for shifting between a first gear position, a second gear position and an intermediate neutral position in a gearbox of a vehicle, the method comprising: moving a coupling mechanism from a first position in which the coupling mechanism is engaged with a first gear wheel of a gearbox, into a neutral position and then into a second position affecting engagement with a second gear wheel, the first and second gear wheels being mounted on an input shaft of the gearbox and the input shaft being disengaged from engine load; controlling speeds of the second gear wheel and the shaft to essentially the same speed before the moving of the coupling mechanism from the neutral position into the second position; and sensing the speed of the vehicle and initiating shifting when the vehicle reaches a predetermined speed.

14. The method as recited in claim 13, wherein, on upshifting, speed control is effected by decelerating the input shaft using a brake connected thereto.

15. The method as recited in claim 14, wherein the brake takes the form of a retarder.

16. The method as recited in claim 14, wherein the brake comprises a multiple disk brake in a main gearbox connected to the gearbox.

17. The method as recited in claim 13, wherein upon upshifting, the speed control is effected by downshifting in a main gearbox connected to the gearbox.

18. The method as recited in claim 13, wherein a main piston, in a piston/cylinder device in which the piston is operationally connected to a coupling mechanism, is brought into an intermediate position for bringing about the neutral position.

19. The method as recited in claim 18, wherein the position of the coupling mechanism is detected and the main piston is made to stop in the neutral position until substantial speed synchronization has been effected.

20. The method as recited in claim 18, wherein, when the coupling mechanism has been detected to be in the neutral position, the main piston is made to stop in the intermediate position by application of a counter-pressure.

21. The method as recited in claim 13, wherein a speed of an output shaft from the gearbox is measured, load to the input shaft of the gearbox is disengaged at a predetermined speed, and the shifting operation is then performed.