The present invention relates to a disk clutch assembly for a marine propulsion device with a pressure-operated actuator for normal operation of the clutch and with emergency actuating means for emergency operation of the clutch in case of an actuator failure.

There are shiftable friction plate clutches known in the art which are actuated by pressure-operated actuators during normal operation. Pressure-operated actuators can be pneumatic or hydraulic actuators. Some of the conventional pressure- operated clutches are equipped with emergency actuating means to enable manual operation in case of a failure of the pressure-operated actuator. Such emergency actuating means in marine propulsion devices are also called“bring home” device or “limb home” device. However, the mechanical emergency actuating means of friction plate clutches in conventional marine propulsion devices are difficult to handle in an emergency situation. Such shiftable disk clutches are often located inside a gearbox housing and the mechanical emergency actuating means have to be operated manually through a housing window with a tool. That makes the handling even more difficult, because the input shaft of the gearbox has to be turned to get access to the emergency actuating means. In some cases this requires an auxiliary electric motor.

An example of a pressure actuated disk clutch with two separate pressure systems and with an additional mechanical emergency actuating device is described in US 6042436 A. This friction plate clutch can be closed by one of the pressure systems or manually by several threaded bolts arranged near the friction plates. When the friction plate clutch has to be closed manually, the clutch together with parts of the power train has to be rotated in order to have access to all threaded bolts with appropriate tools to screw in the threaded bolts.

The aim of the present invention is to avoid the disadvantages of prior art and to provide a disk clutch assembly for a marine propulsion device with a pressure-operated actuator and with emergency actuating means which is easy to handle and which has a simple construction. The invention provides a disk clutch assembly for a marine propulsion device. The disk clutch assembly comprises a disk clutch with friction disks and a pressure- operated actuator to engage and disengage the disk clutch during normal operation. The pressure-operated actuator comprises a first pressure piston arranged in a first pressure cylinder. The first pressure piston and the first pressure cylinder together form a first pressure chamber which can be pressurized through a first pressure supply line.

The disk clutch assembly further comprises emergency actuating means to engage the disk clutch in case of a failure of the pressure-operated actuator.

According to the invention the emergency actuating means comprise a second pressure piston which is arranged in a second pressure cylinder to form a second pressure chamber which can be pressurized through a second pressure supply line. The second pressure piston is equipped with a snap element and the second pressure cylinder is equipped with a groove to lock the second pressure piston in an engaged position. Said groove can be arranged on the inside of the cylinder bore of the second pressure cylinder. Moreover a resilient element is arranged at the disk clutch assembly in such a way to recover possible backlash after the snap element is locked in the engaged position and to ensure a minimum pressure on the clutch disks. That means that a deflection and a resilient force of the resilient element meet certain requirements. A person skilled in the art will easily be able to determine a resilient element with appropriate features for this purpose. The resilient element preferably is a cup spring. Depending on the size of the disk clutch and on the required force, an appropriate size of a cup spring can be used. It is also possible to use several cup springs in a row as resilient element. This way it is possible to apply the required force to the disk clutch by determining and using one or more cup springs with a specific spring characteristic.

The minimum pressure corresponds to a pressure which is required to transmit at least a minimum propeller torque through the disk clutch, so that a marine vessel can be brought home or to a dockyard when the pressure-operated actuator fails. Preferably the snap element is a snap ring which will snap into the groove when the second pressure cylinder reaches the engaged position. The groove can be formed as a circular groove at the inner surface of the second pressure cylinder. In other embodiments there could be one or more spring-biased snap elements which can have other forms than a ring. Correspondingly there can be one or more appropriate grooves to catch and hold the snap elements in the engaged position.

Compared to the conventional solutions with mechanical emergency means the hydraulic solution makes the handling of the disk clutch in case of an emergency simpler and faster. If the pressure-operated actuator fails, the disk clutch can easily be engaged by connecting a little manual external pump to the second pressure supply line and the second piston can be moved to the engaged position by pressurizing the second pressure chamber manually. The snap element will automatically block the second piston in the engaged position and the resilient member ensures that a minimum pressure will be applied to the friction disks of the disk clutch. The minimum pressure must be high enough to close the disk clutch at least to a certain extent, so that the marine propulsion device can again be operated and the vessel can be brought home or to a dockyard to be repaired.

With such a disk clutch assembly it is no more necessary to rotate the disk clutch and parts of the power train in order to gain access to the required emergency actuating means. Moreover there is no additional tool necessary to engage the disk clutch by the emergency engaging means, except a little external pump.

The resilient element can be arranged at a front side of the first pressure piston which is facing towards the friction disks, while the second pressure piston is arranged on a reverse side of the first pressure piston. This way a space-saving layout and easy assembly of the disk clutch assembly can be achieved.

A particularly simple to manufacture is an embodiment, wherein the second pressure cylinder comprises an extended section of the first pressure cylinder. Hence, this embodiment requires only one physical cylinder with two sections, a first section forming the first pressure cylinder and a second section forming the second pressure cylinder. In such an embodiment the first and second pressure cylinders are coaxially to each other. Both pressure cylinders may even be overlapping in axial direction, so that an intermediate section is part of both pressure cylinders.

In another particularly space saving embodiment the second pressure cylinder extends at least partially into a recess of the first pressure cylinder. Hence the second pressure cylinder has a smaller diameter than the first pressure cylinder. This way the axial length of the disk clutch assembly can be reduced. The first and the second pressure cylinder are preferably arranged coaxially to each other in this embodiment as well.

According to a preferred embodiment of the invention the disk clutch assembly comprises a first shaft and a second shaft, wherein the first shaft comprises an outer disk carrier and the second shaft comprises an inner disk carrier of the disk clutch. The first shaft extends through the second shaft, which is formed as a hollow shaft. The first and the second pressure cylinder are preferably part of the first shaft.

The first and the second pressure cylinders can be formed as ring cylinders which are arranged coaxially to a central rotation axis of the disk clutch. Such an arrangement of the parts allow for a very compact layout of the disk clutch assembly.

The invention further covers a gearbox for a marine propulsion device. The gearbox comprising a housing and a disk clutch assembly as described above. A pressure inlet to the second pressure supply line is arranged at the outside of the housing, so that an external pump can easily be connected to actuate the disk clutch in case of failure of the pressure actuated actuator.

The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings, in which:

Fig. 1 shows a disk clutch assembly in a disengaged state in a sectional view according to a first embodiment of the invention; Fig. 2 shows the disk clutch assembly in a disengaged state of Fig. 1 in a different sectional view in a disengaged state;

Fig. 3 shows a drawing detail of the disk clutch assembly of Fig. 1 in a disengaged state of the disk clutch;

Fig. 4 shows the drawing detail of Fig. 3, wherein the disk clutch is engaged by the pressure-operated actuator;

Fig. 5 shows the drawing detail of Fig. 3, wherein the disk clutch is engaged by the emergency actuating means;

Fig. 6 show the emergency actuating means of Fig. 3 in detail;

Fig. 7 shows a disk clutch assembly according to a second embodiment of the invention in a gearbox in a sectional view;

Fig. 8 shows a detail of the second embodiment of Fig. 7 with the disk clutch in a disengaged state;

Fig. 9 shows the detail of Fig. 8 with the disk clutch in an engaged state and

Fig. 10 shows a sectional view of section A - A in Fig. 7.

Fig.1 and Fig. 2 show the same embodiment of a disk clutch assembly 1 wherein the disk clutch 2 is open. Therefore the same elements of the disk clutch assembly 1 have the same reference numbers in both figures. The sectional plane in Fig. 1 runs through a central rotation axis 22 and through a first pressure supply line 7 which are arranged parallel to each other. The sectional plane in Fig. 2 in contrast runs through central rotation axis 22 and through a second pressure supply line 1 1 which are also arranged parallel to each other. The axial and radial directions in this document refer to the central rotation axis 22 of the disk clutch 2. The disk clutch 2 is arranged to selectively connect the first shaft 18 with a second shaft 20. The first shaft 18 is supported by two rolling contact bearings 23, 24 in a housing 33 of a gearbox 32 which can be seen in Fig. 7. The second shaft 20 is formed as a hollow shaft and supported on the first shaft 18 by needle bearings 25 and by axial bearings 26, 27. Both, the first shaft 18 and the second shaft 20 may rotate around a central rotation axis 22. The first shaft 18 extends through the second shaft 20.

The disk clutch 2 comprises an inner disk carrier 21 carrying several inner friction disks 16 and an outer disk carrier 19 carrying several outer friction disks 15. The inner and outer friction disks 15, 16 are conventional friction disks. The inner friction disks 16 are rotationally fixed to the inner disk carrier 21 . The outer friction disks 15 are rotationally fixed to the outer disk carrier 19. The inner friction disks 16 and the outer friction disks 15 are movable in axial direction. In axial direction adjacent to the friction disks 15,16 there is a blocking ring 30 fastened to one end of the outer disk carrier 19. The blocking ring 30 serves to block the friction disks 15,16 when they are pushed in this direction by piston 26. This way the outer disks 15 can be pressed against the inner disks 16 until the disk clutch 2 is engaged by frictional forces between the friction disks 15,16.

The inner disk carrier 21 is part of second shaft 20 and formed as a hollow shaft which is arranged coaxially to the first shaft 18. First shaft 18 extends through the second shaft 20. The second shaft 20 further comprises a pinion 28 to drive another gearwheel which is fixed to an output shaft of the corresponding gearbox. The second shaft 20, the inner disk carrier 21 and pinion 28 are integrally formed as a one- piece element.

A pressure-operated actuator 3 is provided to engage the disk clutch 2 during normal operation. The pressure-operated actuator 3 comprises a first pressure piston 4 which is arranged in a first pressure cylinder 5 to form a first pressure chamber 6.

The pressure chamber 6 can be pressurized through a first pressure supply line 7 which runs through first shaft 18. Pressure-operated actuator 3 in Fig. 1 and Fig. 2 is shown in its retracted and disengaged position, wherein the first pressure piston 4 is located in its leftmost position. In this retracted position the first pressure chamber 6 has its minimum volume and is only a very tiny gap between the first pressure piston 4 and the adjacent second pressure piston 8. In the disengaged position the first pressure piston 4 is pressed by a helical spring 29 to its retracted position away from friction disks 15, 16 of the disk clutch 2.

An extended section of the first pressure cylinder 5 forms a second pressure cylinder 9 which is part of emergency actuating means 8, 9, 10, 1 1 . The actuating means 8, 9, 10, 1 1 further comprise a second pressure piston 8 which is arranged in said second pressure cylinder 9 to form a second pressure chamber 10. The second pressure chamber 10 can be pressurized through a second pressure supply line 1 1 which can be seen in Fig. 2. The second pressure supply line 1 1 is separate and independent from the first pressure supply line 7. The first and the second pressure supply lines 7 and 1 1 at least partly run through the first shaft 18 parallel to each other and parallel to the central rotation axis 22. The first and the second pressure cylinder 5, 9 are arranged at the first shaft 18. Both pressure cylinders 5 and 9 are ring cylinders which are arranged coaxially to the central rotation axis 22 of the disk clutch 2.

The second pressure piston 8 is equipped with a snap element 12, namely a snap ring. A groove in the cylinder bore of the second pressure cylinder 9 is provided, to lock the snap element 12 and the second pressure piston 8 in an engaged position.

A resilient element 14 in the form of a cup spring is arranged between the first pressure piston 4 and the disks 15, 16. The resilient element 14 is arranged at a front side of the first pressure piston 4 which is facing towards the friction disks 15, 16, while the second pressure piston 8 is arranged on a reverse side of the first pressure piston 4.

The resilient element 14 has two functions. Firstly it recovers possible backlash at the snap element 12 as soon as the snap element 12 has been locked in groove 13, after the second pressure piston 8 has been moved to the emergency engagement position. In this situation the resilient element 14 retained by the snap ring 12 ensures a minimum pressure on the friction disks 15, 16 to transmit at least a minimum propeller torque. Secondly it enables smooth engagement of the disk clutch 2 during normal operation. As a result harsh engagement of the disk clutch 2 is avoided when actuating pressure acts on first pressure piston 4 during normal operation.

Fig. 3 shows an enlarged section of Fig. 1 with the disk clutch 2 being open, i.e. in the disengaged state. The first pressure piston 4 is hold in its utmost left-hand position by helical spring 29. The resilient element 14, i.e. the cup spring 14 is unstressed. Hence, there is no pressure between the outer friction disks 15 and the inner friction disks 16, so that the first shaft 18 and the second shaft 20 may stand or rotate independently from one another.

Whereas Fig. 4 shows the enlarged section with the disk clutch 2 being closed, i.e. in the engaged state. The engagement of disk clutch 2 in Fig. 4 has been effected by means of pressure operated actuator 3 which is used during normal operation. For this the first pressure chamber 6 has been pressurized via first pressure supply line 7. Consequently the first pressure piston 4 has been moved towards the friction disks 15, 16 pressing the cup spring 14 onto the friction disks 15, 16 and all together against the blocking ring 30. Hence, the disk clutch 2 is closed and a driving torque can be transmitted from the first shaft 18 to the second shaft 20. The first pressure supply line 7 consists of axial and radial bores in the first shaft 18.

Fig. 5 shows again the enlarged section with the disk clutch 2 being closed, i.e. in the engaged state. However in Fig. 5 the engagement of disk clutch 2 has been effected by means of the emergency actuating means 8, 9, 10 and 1 1 . For this the second pressure chamber 10 has been pressurized via second pressure supply line 1 1. This can be done for example by a little external pump which can be connected to the second pressure supply line 1 1. Consequently the second pressure piston 8 has been moved towards the friction disks 15, 16 pressing the cup spring 14 onto the friction disks 15, 16 and all together against the blocking ring 30. Hence, the disk clutch 2 is closed and a driving torque can be transmitted from the first shaft 18 to the second shaft 20. The second pressure supply line 1 1 consists of axial and radial bores in the first shaft 18 as well. The second pressure piston 8 is equipped with snap ring 12, in order to hold the disk clutch 2 engaged, even so the external pump has been removed and there is no more pressure in the second pressure supply line 1 1 . As soon as the second pressure piston 8 has been moved in its engaged position, the snap ring 12 will latch in groove 13. This can be seen in detail in Fig. 6. In this situation the force of the resilient element 14 in form of the spring-biased cup spring recovers possible backlash and effects enough pressure on the friction disks 15 and 16 to transmit a driving force from the first shaft 18 to the second shaft 20 or vice versa. The groove 13 is formed in a way that a safe hold of the snap ring 12 in one axial direction is ensured, so that the engaged disk clutch 2 may not be disengaged inadvertently. In the opposite direction however the snap ring 12 may be moved, in order to allow for an easy disassembly and rearm of the emergency actuating means. For this the groove 13 has an asymmetric cross-sectional shape.

Fig. 7 shows a second embodiment of the invention. The general layout of the disk clutch assembly 1 is the same than in the first embodiment described above. Therefore the same elements of the disk clutch assembly 1 have the same reference numbers. The difference between the first and second embodiments is the arrangement of the second pressure cylinder 9 in relation to the first pressure cylinder 5. While in the first embodiment the two pressure cylinders 5 and 9 are arranged one behind the other, in the second embodiment the second pressure cylinder 9 extends partially into a recess 17 of the first pressure cylinder 5. Hence, in the second embodiment the two pressure cylinders 5 and 9 are arranged overlapping in axial direction . This allows a particularly short layout of the disk clutch assembly 1 in axial direction.

Fig. 7 further shows the arrangement of the disk clutch assembly 1 in the housing 33 of a gearbox 32. The housing 33 of gearbox 32 is shown only partially in Fig. 7. A pressure inlet 34 to the second pressure supply line 1 1 is arranged at the outside of the housing 33. The pressure supply line 1 1 extends from the pressure inlet 34 through a pressure supply duct 35 in the housing 33 and through bores in the first shaft 18 to the second pressure chamber 10. Pressure supply duct 35 extends radially from the pressure inlet 34 to a circumferential groove 36 in first shaft 18. The cir- cumferential groove 36 serves for pressure transfer from the stationary pressure supply duct 35 to the rotatable part of pressure supply line 1 1 in the first shaft 18.

Fig. 8 and Fig. 9 show detailed views of the second embodiment. In Fig. 8 the first and the second pressure pistons 4 and 8 are in the left-hand retracted position. The resilient element 14 is unstressed and disk clutch 2 is disengaged.

In Fig. 9 the second pressure chamber 10 has been pressurized and second pressure piston 8 together with first pressure piston 4 has been moved to the right in an engaged position.

The second pressure piston 8 of the second embodiment is also equipped with a snap ring 12, in order to hold the second pressure piston 8 in the engaged position and to keep disk clutch 2 engaged, when there is no more pressure in the second pressure supply line 1 1 . As soon as the second pressure piston 8 has been moved in its engaged position, the snap ring 12 will latch in groove 13. Than the force of spring-biased cup spring 14 recovers possible backlash and effects enough pressure on the friction disks 15, 16 to transmit a driving force from the first shaft 18 to the second shaft 20 or vice versa.

The sectional view along plane A - A in Fig. 10 shows first shaft 18 arranged inside the housing 33. In particular it shows three bores 7, 1 1 and 37 which are arranged parallel to each other inside first shaft 18. The first bore is the first pressure supply line 7 which is connected to the first pressure chamber 6 of the pressure-operated actuator 3. The second bore is the second pressure supply line 1 1 , which connects the pressure inlet 34 at the outside of housing 33 with the second pressure chamber 10. In the sectional view of Fig. 10 it can be seen that pressure supply duct 35 in housing 33 is connected to the second pressure supply line 1 1 via circumferential groove 36 in the first shaft 18. The third bore in first shaft 18 is a lubrication bore 37 which connects a lubrication oil pump with different lubrication points in the gearbox 32, as for example the rolling contact bearings 23 and 24. Reference Numeral disk clutch assembly

disk clutch

pressure-operated actuator

first pressure piston

first pressure cylinder

first pressure chamber

first pressure supply line

second pressure piston

second pressure cylinder

second pressure chamber

second pressure supply line

snap element

groove

resilient element

outer friction disks

inner friction disks

recess

first shaft

outer disk carrier

second shaft

inner disk carrier

central rotation axis

rolling contact bearing

rolling contact bearing

needle bearings

axial bearing

axial bearing

pinion

helical spring

blocking ring

ramp gearbox

housing

pressure inlet pressure supply duct circumferential groove lubrication bore