Transmission with at least one hydraulically operated clutch

Abstract

A transmission with at least one hydraulically actuated clutch, wherein the clutch forms a piston chamber (3) with a piston (1) and a cylinder (2), wherein this piston chamber (3) is connected to a pressure medium reservoir (6) via a drain valve, and the piston chamber (3) can be pressurized with pressure medium from a pressure medium source via a pressure medium supply (4), and the pressure medium supply (4) can be connected selectively to the pressure medium reservoir (6) or the pressure medium source via a valve (8), wherein when the pressure medium supply (4) is connected to the pressure medium reservoir (6) by means of the valve (8), a minimum pressure and / or a minimum quantity of pressure medium is present in the pressure medium supply (4), wherein the minimum pressure and / or the minimum quantity of pressure medium is lower than the pressure or the quantity of pressure medium which actuates the drain valve in the closing direction, characterized in that the valve (8) is designed such thatthat a leakage of a piston of the valve (8) is directed from the pressure medium source to the pressure medium supply (4).,

Description

[0001] The invention relates to a transmission with at least one hydraulically actuated clutch according to the type defined in more detail in the preamble of claim 1.

[0002] Generic transmissions are used, for example, in work machines such as wheel loaders or dump trucks. This type of transmission has a large center distance between the input shaft and the output shaft, which means that the transmission contains many spaced shafts with couplings, but has a small axial extension. To prevent the couplings from building up rotational pressure, drain valves are used in the couplings. When the coupling is not actuated, the pressure fluid flows out of the pressure chamber via the drain valve.

[0003] DE 199 15 557 A1, DE 196 42 305 A1 and DE 39 07 993 A1 disclose a hydraulically actuated clutch with a drain valve.

[0004] The present invention is based on the object of improving the hydraulically actuated clutch according to the prior art.

[0005] The problem is solved by a generic hydraulically actuated clutch which also has the characterising features of the main claim.

[0006] According to the invention, the piston chamber of the clutch and the pressure medium supply to the piston chamber of the clutch cannot empty to such an extent that the pressure medium in the pressure medium supply is replaced by ambient air. As a result, it is not necessary to displace this air from the piston chamber via the drain valve when the clutch is engaged. This has the particular advantage of eliminating pressure fluctuations such as those present in the prior art. In the prior art, the air content present in the piston chamber and in the pressure medium supply is often not reliably expelled by the pressure medium when the clutch is engaged. This leaves a residual air content which frequently leads to pressure fluctuations since this residual air content is compressible. The solution according to the invention prevents residual air from remaining when the clutch is engaged due to premature closing of the drain valve.This is achieved by keeping the amount of air in the clutch chamber and the pressure medium supply as low as possible. This is achieved by having pressure medium flow through the pressure medium supply and the piston chamber when the clutch is deactivated. The volume flow of the pressure medium in the appropriate quantity reliably transports the air in the pressure medium supply and the piston chamber through the drain valve and ensures that the remaining air content is very low before the next gearshift. The volume flow must therefore be large enough to reliably remove the air from the pressure medium supply and the piston chamber, but the volume flow must not be so large that the drain valve closes or the overall efficiency of the transmission is drastically reduced.

[0007] Preferably, the pressure medium supply and the piston chamber are permeated by the leakage created by the valve used to engage and disengage the clutch. The leakage can be realized, for example, through a gap between the piston and the cylinder of the valve. For this purpose, the piston preferably has a diameter step, meaning that one area of ​​the piston has a smaller diameter than the adjacent area, with a defined leakage being created in the area of ​​the smaller diameter, which is fed to the pressure medium supply and the clutch.

[0008] In a further embodiment of the invention, a pressure relief valve is arranged between the valve and the pressure fluid reservoir, maintaining a defined leakage pressure at the valve. This pressure arises because the leakage from the valve can only be discharged to the pressure fluid reservoir if the pressure exceeds the pressure of the pressure relief valve. Since the valve is switched in such a way that, when the clutch is deactivated, the leakage from the valve is directed to the pressure fluid supply and the piston chamber, the pressure set by the pressure relief valve is present in the pressure fluid supply and the piston chamber. The pressure fluid supply and the piston chamber are thus reliably flowed through.

[0009] In a further embodiment of the invention, the pressure fluid reservoir is arranged above the coupling. This ensures that a starting pressure generated by the height difference is present at the leakage return to the pressure fluid reservoir, and the leakage can be fed to the pressure fluid supply and the coupling at the same pressure.

[0010] In a further embodiment of the invention, several couplings and several valves assigned to the couplings are provided, wherein the valves are arranged in a common housing, which is also referred to as a hydraulic control housing. The housing is sealed liquid-tight to the outside and forms a closed space with the valves. From this closed space, only the connections for the couplings as well as the pressure medium supply and return to the pressure medium reservoir are accessible. If a pressure relief valve is arranged at the outlet of the housing towards the pressure medium reservoir, the leakage pressure of all valves in the housing can be kept at the same level. The leakage from the valves thus ensures that all couplings are evenly flowed through.

[0011] A defined leakage quantity and a defined leakage pressure, which is supplied to the pressure medium supply and the piston chamber when the clutch is switched off, prevents an excessive amount of air from remaining in the piston chamber when the hydraulic clutch is switched on, thus reliably avoiding pressure fluctuations.

[0012] Further features can be found in the figure description.

[0013] It shows Fig. 1 a hydraulic diagram of the clutch arrangement according to the invention; Fig. 2 a hydraulic diagram of the clutch arrangement according to the invention with a vibration damper; Fig. 3 a hydraulic diagram of the clutch according to the invention, in which each clutch is individually controlled. Fig. 4 a hydraulic diagram of the clutch arrangement according to the invention with a pressure medium reservoir arranged above the clutches; Fig. 5 a coupling diagram of the coupling arrangement according to the invention with a central pressure relief valve on the hydraulic control; Fig. 6 a coupling diagram of the coupling arrangement according to the invention with a pressure relief valve for each valve. Fig. 1:

[0014] A piston 1 of a hydraulically actuated clutch forms a piston chamber 3 with the cylinder 2. The piston chamber 3 is connected to the pressure medium supply 4. The piston 1 is connected to a plate pack of a multi-plate clutch (not shown). If there is pressure in the piston chamber 3, the piston 1 presses against the spring 5 and compresses the plate pack so that the clutch is engaged and can transmit torque. If the piston chamber 3 is depressurized, the spring 5 pushes the piston 1 back and the clutch is actuated in the opening direction. The piston chamber 3 is connected to a pressure medium reservoir 6 via a drain valve (not shown). Pressure medium is fed into the supply lines 7 from a pressure medium source (not shown). The pressure medium from the pressure medium source reaches the piston chamber 3 via the valve 8. For this purpose, the valve 8 is controlled by the control valve 9.The valve 8 is designed in such a way that when the clutch is not actuated, it is in the state which is shown in the . Fig. 1, so much leakage occurs between the piston and the cylinder of valve 8 that pressure medium is directed via the pressure medium supply 4 into the piston chamber 3 and from there via the drain valve into the pressure medium reservoir. For this purpose, there is a connection in valve 8 through which the leakage is directed into the pressure medium supply 4. To prevent the leakage from flowing directly via valve 8 into the pressure medium reservoir 6, a pressure relief valve 10 is arranged between valve 8 and pressure medium reservoir 6. The pressure relief valve 10 and the amount of leakage through the appropriate selection of the diameter in the piston of valve 8 are designed such that the drain valve is not yet actuated in the closing direction. As a result, when the clutch is not actuated, sufficient pressure medium can flow through the pressure medium supply 4 and the piston chamber 3 to keep corresponding air components away from the piston chamber 3. Fig. 2:

[0015] The Fig. 2 differs from the Fig. 1 in that a damping unit with a damping piston 11, which interacts with a spring 12, is additionally present in the control line 13. The damping piston 11 dampens the control oscillations so that the valve 8 can be controlled precisely. Fig. 3:

[0016] The Fig. 3 differs from the Fig. 1 in that several couplings with several associated valves 8 are shown. The valves 8 are arranged in a liquid-tight housing 14, whereby the leakage of the valves 8 must be directed via a common return line 15 into the pressure medium reservoir 6. The solution according to the Fig. 3 does not have a pressure relief valve 10 like the Fig. 1 and Fig. 2, however, the static pressure, i.e. the pressure acting on the clutch when the clutch is disengaged, is regulated individually for each clutch via control line 13. The regulation of the pressure medium quantity and the pressure medium pressure is designed in such a way that the drain valve (not shown) is not actuated in the closing direction. Fig. 4:

[0017] The solution after the Fig. 4 differs from the solution according to the Fig. 3 in that the pressure medium reservoir 6 is arranged above the couplings or the piston chambers 3. This ensures that the piston chambers 3 always remain sufficiently filled with pressure medium. Fig. 5:

[0018] The Fig. 5 differs from the Fig. 4 in that a pressure relief valve 10 is arranged between the housing 14 and the pressure medium reservoir 6, whereby the pressure medium chambers 3 are now directly connected to the pressure medium reservoir 6 via the pressure medium supply lines 4. The leakage of all valves 8 thus ensures that the pressure medium chambers 3 remain sufficiently filled with pressure medium. Fig. 6:

[0019] The Fig. 6 differs from the Fig. 5 in that each valve 8 has its own pressure relief valve 10, by means of which the leakage pressure or the return pressure or even the pressure in the pressure medium supply 4 can be individually adjusted. This has the particular advantage that different drain valves, different coupling heights, or other different designs of the lines, couplings, and valves are possible. Reference symbol 1 piston 2 cylinders 3 Piston chamber 4 Pressure medium supply 5 spring 6 Pressure medium reservoir 7 Supply line 8 valve 9 Control valve 10 Pressure relief valve 11 Damping piston 12 springs 13 Control line 14 housings 15 Return line

Claims

[1] A transmission with at least one hydraulically actuated clutch, wherein the clutch forms a piston chamber (3) with a piston (1) and a cylinder (2), wherein this piston chamber (3) is connected to a pressure medium reservoir (6) via a drain valve and the piston chamber (3) can be pressurised with pressure medium from a pressure medium source via a pressure medium supply (4), and the pressure medium supply (4) can be connected selectively to the pressure medium reservoir (6) or the pressure medium source via a valve (8), wherein when the pressure medium supply (4) is connected to the pressure medium reservoir (6) by means of the valve (8), a minimum pressure and / or a minimum quantity of pressure medium is present in the pressure medium supply (4), wherein the minimum pressure and / or the minimum quantity of pressure medium is lower than the pressure or the quantity of pressure medium which actuates the drain valve in the closing direction, characterized bythat the valve (8) is designed such that a leakage of a piston of the valve (8) is directed from the pressure medium source to the pressure medium supply (4). [2] Transmission according to claim 1, characterized by that the pressure medium reservoir (6) is arranged above the coupling. [3] Transmission according to claim 1, characterized by that a pressure relief valve (10) is arranged between the valve (8) and the pressure medium reservoir (6). [4] Transmission according to claim 1, characterized by that several couplings can be controlled by several valves (8) and the valves are arranged in a closed housing (14), wherein this housing (14) is connected to the pressure medium reservoir (6) via a return line (15) and the leakage of the valves (8) flows into the closed housing (14). [5] Transmission according to claim 4, characterized bythat a pressure relief valve (10) is arranged between the return line (15) of the housing (14) and the pressure medium reservoir (6). [6] Transmission according to claim 4, characterized by that a pressure relief valve (10) is arranged between each valve (8) and the pressure medium reservoir (6). [7] Transmission according to claim 1, characterized by that the valve (8) is controlled by means of a control device (9) so that a defined pressure medium pressure remains in the coupling. [8] Transmission according to claim 1, characterized by that the transmission has a plurality of spaced shafts and gears, with couplings arranged on the shafts, whereby the radial extent of the transmission is greater than the axial extent of the transmission. [9] Use of the transmission according to claim 1 in a wheel loader or dumper.

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