CLUTCH ASSEMBLY

Abstract

A clutch assembly may have an axially slidable first plate, an axially fixed second plate disposed opposite the first plate, and a clutch pack arranged between the first plate and the second plate. The clutch pack may have a number of axially slidable consecutively arranged friction plates and separator plates. The assembly may also have an actuator axially movable between a first position and a second position, where, in the first position, the clutch pack is opened and, in the second position, the clutch pack is closed and the friction plates are frictionally engaged. The assembly may also have a return spring configured to bias the actuator in a direction away from the clutch pack towards the first position. The assembly may also have an engagement spring element configured to exert an elastic force on the clutch pack.

Claims

1.-14. (canceled)

15. A clutch assembly, comprising: an axially slidable first plate, an axially fixed second plate disposed opposite the first plate, a clutch pack arranged between the first plate and the second plate, wherein the clutch pack comprises a plurality of axially slidable consecutively arranged friction plates and separator plates, an actuator axially movable between a first position and a second position, wherein, in the first position, the clutch pack is opened and, in the second position, the clutch pack is closed and the friction plates are frictionally engaged, a return spring configured to bias the actuator in a direction away from the clutch pack towards the first position, and an engagement spring element configured to exert an elastic force on the clutch pack.

16. The clutch assembly of claim 15, wherein the elastic force exerted on the clutch pack by the engagement spring element comprises an elastic axial force and an elastic shear force.

17. The clutch assembly of claim 15, wherein the engagement spring element is configured to exert the elastic force on the clutch pack via the first plate.

18. The clutch assembly of claim 15, wherein, in the second position, the actuator is configured to push the first plate against the clutch pack.

19. The clutch assembly of claim 15, wherein the friction plates are at least partially covered with a friction material.

20. The clutch assembly of claim 19, wherein the friction plates are at least partially covered with the friction material when the elasticity of the engagement spring element is higher than the elasticity of the friction material of the friction plates.

21. The clutch assembly of claim 20, wherein the engagement spring element is at least partially arranged inside a recess of the actuator.

22. The clutch assembly of claim 15, wherein the engagement spring element is arranged between the actuator and the first plate.

23. The clutch assembly of claim 15, wherein the engagement spring element is arranged between the clutch pack and the second plate.

24. The clutch assembly of claim 15, wherein the engagement spring element is an integral part of the actuator.

25. The clutch assembly of claim 23, wherein the engagement spring element is configured as an elastically formable material layer of at least one of an elastomer and a spring element between two stiff components of the actuator or the second plate.

26. The clutch assembly of claim 15, wherein the engagement spring element is an integral part of the second plate.

27. The clutch assembly of claim 15, wherein the engagement spring element comprises a plurality of spring elements arranged between the friction plates and the separator plates of the clutch pack.

28. The clutch assembly of claim 15, wherein the clutch assembly is a wet clutch assembly or a dry clutch assembly.

30. The clutch assembly of claim 15, wherein the actuator is a piston controlled mechanically or pneumatically or electrically or magnetically or hydraulically.

Description

DESCRIPTION OF THE FIGURES

[0035] FIG. 1 shows a section view of an exemplary wet clutch assembly with an engagement spring,

[0036] FIG. 2 shows a section view of another example of a wet clutch with an engagement spring variant,

[0037] FIG. 3 shows a section view of another example of a wet clutch with an engagement spring variant, and

[0038] FIG. 4 shows a section view of another example of a wet clutch with another engagement spring variant.

DETAILED DESCRIPTION

[0039] In FIG. 1, a wet clutch assembly is illustrated in a sectional view. The clutch assembly comprises a first plate 1 and a second plate 2. A clutch pack 3 is arranged between the first and the second plate. The first plate 1 and the second plate 2 have an annular shape and are arranged centered to a clutch axis A. The clutch pack 3 comprises a plurality of axially slidable, consecutively arranged friction plates 301 and separator plates 302. The friction plates 301 are rotationally fixedly coupled to a shaft 4, for example, via internal splines engaged with external splines of the shaft. The friction plates 301 have friction surfaces to increase the coefficient of friction. The friction surfaces may comprise graphite, carbon fiber, organic, powder metallurgic, aramid fiber and/or ceramic materials. The separator plates 302 are interlocked with a clutch drum 5. The separator plates 302 may comprise steel (or essentially equivalent materials). An actuator 6 is arranged adjacent to the first plate 1 such that the actuator may push the first plate towards the second plate, thereby compressing the clutch pack 3 such that the separator plates 302 and the friction plates 301 engage frictionally. The actuator 6 may be actuated hydraulically by oil pressure.

[0040] As shown in FIG. 1, the actuator 6 is a piston. When actuated, the piston of the clutch needs to first move a certain distance to close all the clearances. The zero clearance point is called the kiss point. No torque is transferred yet, as no contact pressure exists between the friction plates 301 and separator plates 302. Then, the pressure is gradually increased to increase the torque transfer. As such, the rotational speeds of the friction plates 301 and the separator plates 302 are synchronized. When frictionally engaged, the clutch drum 5 and the shaft 4 may rotate with the same speed. When synchronized, the pressure may be further increased to prevent slipping. At this point, typically, the clutch is said to be closed.

[0041] The shaft 4 may be a hollow shaft. A return spring 7 applies a spring pressure onto the actuator 6 to disengage the friction plates. The return spring 7 pushes the actuator 6 away from the clutch pack 3 in a direction shown by arrow 71. The return spring may be arranged in a cavity of the hollow shaft 4.

[0042] The actuator comprises a recess 61 pointing towards the first plate 1. An engagement spring 8 is arranged in the recess for applying a pressure onto the first plate. This leads to a more uniform distribution of the contact pressure between the friction plates 301 and separator plates 302. Further, the elasticity in the clutch is not a requirement of the friction material anymore, and more efficient or typically less elastic friction materials can be selected in comparison with a wet clutch without engagement spring.

[0043] Due to the engagement spring 8, the kiss point may be less discrete. As such, clutch tuning may be simplified and possibly also the calibration interval may be extended. A less sensitive kiss point may improve shifting quality by reducing torque variations in case of kiss point errors.

[0044] Typically, a proportional valve is used to provide oil pressure for actuating the actuator 6. The proportional valve requires a certain flow rate for a qualitative pressure control. Typically, an accumulator is mounted between the clutch and the proportional valve to absorb that flow. With the engagement spring 8, this accumulator could be downsized or eliminated.

[0045] The actuator 6 and the return spring 7 are coupled to a shaft 9 disposed in the hollow shaft (Hub) 4. The clutch drum 5 is coupled to a housing 10 coupled to the shaft 9. Hub 4 is supported by shaft 9 via bearings but rotationally not coupled.

[0046] The clutch is a wet clutch. The wet clutch is cooled by lubrication oil that flows through grooves in the friction material of the friction plates 301 when the wet clutch is closed. In open condition, the lubrication oil can flow in between the separator plates 302 and friction plates 301.

[0047] In open condition, the lubrication oil reduces touching of the friction plates 301 and the separator plates 302 and thus reduces power loss by friction, namely clutch drag. Nevertheless, some clearance is needed between the separator plates 302 and friction plates 301 in open condition.

[0048] FIG. 2 shows a clutch assembly in a sectional view. The clutch assembly is essentially similar to the clutch assembly of FIG. 1, wherein the piston 6 and an engagement spring assembly comprising the engagement spring 8′ have a different design.

[0049] The clutch assembly comprises a first plate 1 and a second plate 2. A clutch pack 3 is arranged between the first and the second plate 1, 2. The first plate 1 and the second plate 2 have an annular shape and are arranged centered to a clutch axis A. The clutch pack 3 comprises a plurality of axially slidable, consecutively arranged friction plates 301 and separator plates 302. The friction plates 301 are rotationally fixedly coupled to a shaft 4, for example via internal gears engaged with external gears of the shaft. The friction plates 301 have friction surfaces to increase the coefficient of friction. The friction surfaces may comprise graphite, carbon fiber, organic, powder metallurgic, aramid fiber and/or ceramic materials. The separator plates 302 are interlocked with a clutch drum 5. The separator plates 302 may comprise steel (or essentially equivalent materials). An actuator 6 is arranged adjacent to a plate 1′ such that the actuator may push the plate 1′ towards the second plate 2, thereby compressing the clutch pack 3 such that the separator plates 302 and the friction plates 301 engage frictionally. The actuator 6 may be actuated hydraulically by oil pressure.

[0050] The operation of the actuator corresponds to the operation of the actuator shown in Fig.1, which is referenced here.

[0051] The shaft 4 is a hollow shaft. The return spring 7 applies a spring pressure onto the actuator 6 to disengage the friction plates. The return spring 7 pushes the actuator 6 away from the clutch pack 3 in a direction shown by arrow 71. The return spring may be arranged in a cavity of the hollow shaft 4.

[0052] An engagement spring 8 is arranged between the plate 1′ and the first plate 1, the first plate 1 being arranged adjacent to the clutch pack 3 for applying a pressure onto the clutch pack. The engagement spring 8 of FIG. 2 is a (waved or conical) steel spring or elastomeric element positioned between the 1′ and the first plate 1. The first plate 1 is slidably arranged between the engagement spring 8 and the clutch pack 3. The force applied onto the clutch pack 3 via plate 1 leads to a more uniform distribution of the contact pressure between the friction plates 301 and separator plates 302. Further, the elasticity in the clutch is not a requirement of the friction material anymore, and more efficient or stiffer friction materials can be selected in comparison with a wet clutch without engagement spring.

[0053] Due to the engagement spring 8, the kiss point may be less discrete. As such, clutch tuning may be simplified and possibly also the calibration interval may be extended. A less sensitive kiss point may improve shifting quality by reducing torque variations in case of kiss point errors.

[0054] In FIG. 3, a variant of the clutch pack of the aforementioned figures is shown. The same reference signs were used for recurring features. The engagement spring of FIG. 3 is arranged in a recess 61 formed in the actuator 6. For illustration purposes, only one separator plate 302 of the clutch pack 3 is illustrated, wherein the design of the clutch pack 3 corresponds to that of the previous figures including a plurality of separator plates 302 and friction plates 301. The engagement spring 8 applies a force onto the clutch pack 3 via the first plate 1. The first plate 1 of FIG. 3 comprises a u-shaped part. The engagement spring 8 applies a force onto the u-shaped part 1 that transmits the force onto the clutch pack. When the actuator 8 is moved towards the clutch pack 3, the return spring 7 is compressed and the actuator 6 applies a force onto the u-shaped part 1 to compress the clutch pack 3.

[0055] In FIG. 4, a variant of the clutch pack of the aforementioned figures is shown. The clutch assembly of FIG. 4 is essentially similar to the clutch assembly of FIG. 1, wherein the engagement spring 8 is an elastomer arranged in the recess 61 of the actuator 6. The same reference signs were used for recurring features. Due to the engagement spring 8, in FIG. 4 being an engagement elastomer, the kiss point is less discrete. As such, clutch tuning is simplified and the configuration interval can be extended. A less sensitive kiss point improves shifting quality by reducing torque variations in case of kiss point errors. A simple hydraulic circuit can be used. Expensive hydraulic components such as accumulators or complex control strategies can be removed and this will benefit the overall cost efficiency of a transmission.

[0056] The clutch assemblies of FIGS. 1-3 have a longer extension along the axis A compared to the clutch assembly of FIG. 4. Thus, the design of FIG. 4 allows for a more compact clutch assembly. In FIG. 4, a hydraulic conduit 11 is shown. A fluid, in particular oil, can be inserted into a sealed recess 12 in which the actuator 6 is located to operate the actuator 6.

[0057] The clutch assemblies shown in FIGS. 1-4 are wet clutch assemblies. The wet clutch is cooled by lubrication oil that flows though grooves in the friction material when the wet clutch is closed. In open condition, the lubrication oil can flow in between the plates. In open condition the lubrication oil has a second function: it reduces touching of the friction plates and the separator plates and thus reduces power loss by friction, namely clutch drag. Nevertheless, some clearance is needed between the plates in open condition.