RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 371 as a U.S. National Phase application of application no. PCT/EP2022/063033, filed on 13 May 2022, which claims the benefit of German Patent Application no. 10 2021 206 095.1, filed 15 Jun. 2021, the contents of which are hereby incorporated herein by reference in their entireties.

FIELD OF THE DISCLOSURE

The present invention relates to a marine drive unit with a cooling oil circuit.

BACKGROUND

One example of a marine drive unit with a lubricating oil supply system and with means for the cooling of the lubricating oil has been disclosed in WO 03/093106 A1. This document describes outboard drive unit for boats with a first bevel gearing enclosed in an underwater housing and a second bevel gearing enclosed in a gear housing. With the aid of a mounting element joined to the underwater housing and the gear housing, the drive unit can be mounted in an opening in the bottom of a boat hull, with the underwater housing on the outside and the gear housing on the inside of the hull. The mounting element forms a housing which defines, firstly, an oil reservoir for the oil of the drive unit and, secondly, a surrounding chamber through which engine cooling water flows and which is used for cooling the oil in the reservoir.

SUMMARY

The purpose of the present invention is to provide an improved marine drive unit with sufficient cooling capacity for the oil inside the marine drive unit.

This purpose is achieved by a marine drive unit according to the present disclosure. Further embodiments will be apparent in light of the description and claims.

The present invention provides a marine drive unit comprising an upper bevel gear set and a lower bevel gear set, wherein the upper bevel gear set is connected to the lower bevel gear set by a drive shaft which extends in vertical direction. Such marine drive units are called POD-drive, Z-drive or azimuth thruster. The drive power is usually transmitted from an inboard engine with a horizontal output shaft via the vertical drive shaft to a horizontal propeller shaft. An electric motor can also be used instead of the engine. A horizontal input shaft of the marine drive unit is arranged to be coupled to the output shaft from the inboard engine or motor. The upper bevel gear set which drivable connects the horizontal input shaft to the vertical drive shaft can be combined with a reversing transmission, comprising wet disc clutches. The oil for actuating such forward/reverse-clutches is also used as lubricating oil for both the upper bevel gear set and the lower bevel gear set in an underwater housing.

A first oil pump of the marine drive unit is arranged to supply oil to the upper bevel gear set. The first oil pump delivers oil for cooling and lubricating the upper bevel gear set. Said first oil pump may as well be used to supply pressure for the pressure operated forward/reverse-clutch which is provided to reverse the rotational direction of the drive shaft with regard to an input shaft of the marine drive unit. The pressure operated forward/revers-clutch can be a multiple disk clutch with a hydraulic actuation.

Additionally, a second oil pump is arranged to feed a cooling oil circuit. Hence, there is one pressure and lubrication oil circuit which is feed by the first oil pump and another cooling oil circuit, which is feed by the second oil pump. Both said oil circuits can be operated with the same oil. Both said oil circuits can be feed from one single oil reservoir. For this, the first and the second oil pump can be connected to one common oil reservoir. The lubrication oil circuit containing the first oil pump can be used for the pressure supply to actuate the forward/reverse-clutch and for the lubrication and cooling of the upper bevel gear set. The function of the cooling oil circuit is the recirculation and cooling of the oil in the lower part of the marine drive unit. The pump capacity and pressure can be chosen and adjusted separately for the first and second pump. There-fore, an optimum layout for each pump and its requirements in view of capacity and pressure head can be achieved.

The second oil pump can be located at the lower end of the drive shaft to suck oil from an oil reservoir through a bore in the drive shaft and to pump it through a first opening at the second oil pump back into the oil reservoir. Hence, the oil is sucked from an upper region in the oil reservoir through the bore in the drive shaft and delivered back into the oil reservoir through the first opening at the lower end of the drive shaft. This way an oil circuit is executed when the drive shaft is rotating. The bore is preferably positioned coaxially to the centerline of the drive shaft. Preferably at least one first opening is positioned near the lower bevel gear set to ensure sufficient lubrication and cooling of the lower gear set. Although the lower bevel gear set may be arranged inside the oil reservoir and be completely submerged by the oil.

In another embodiment the direction of oil flow in the oil circuit can be reversed with regard to the oil circuit described above. In this case the second oil pump at the lower end of the drive shaft can suck oil from an oil reservoir through the at least one first opening at the second oil pump and pump it upwards through the bore in the drive shaft and through the second opening back to the oil reservoir.

In one embodiment the drive shaft can be arranged at least partially inside an underwater housing of the marine drive unit, wherein an inside space of the underwater housing forms the oil reservoir. The underwater housing is positioned under a waterline. The waterline refers to a line on a hull of the boat that is parallel to the water surface when the boat is afloat in a normal position. The underwater housing being filled with oil has the effect, that the oil will be continuously cooled by the ambient water through the underwater housing wall. Hence, the oil circuit described above is working as a cooling oil circuit. A specific water-cooling circuit, as it is usually part of conventional marine drive units, is not necessary anymore.

The drive shaft may be a multi-part component and comprise an upper shaft section and a lower shaft section. The upper shaft section can be a pinion shaft of a pinion from the upper bevel gear set. A pinion of the upper bevel gear set and the upper shaft section can be manufactured from one piece.

Said bore in the drive shaft can be a central bore in the lower shaft section. At least one second opening between the oil reservoir and the bore may be positioned between the upper and lower shaft section. Thus, the second opening connects the oil reservoir outside the drive shaft with the bore inside the drive shaft. Preferably, the upper shaft section can be connected to the lower shaft section by a sleeve. The sleeve can comprise the at least one second opening. Such a second opening in the sleeve can form an oil intake or an oil outlet, depending on the direction of the oil flow in the cooling oil circuit. Preferably several second openings are arranged around the cylindrical circumference of said sleeve.

The second oil pump may be carried out in the form of a screw pump. Hence, the second oil pump can comprise a pump screw which is arranged co-axially to the bore in the drive shaft. The pump screw can be mounted to the lower end of the drive shaft. This type of second oil pump may also comprise a screw pump jacket which can be mounted to the lower end of the drive shaft and carries the pump screw inside. Such a type of screw pump can be pre-assembled and tested independently from the drive shaft. This way quick and easy final assembly in the marine drive unit and a reliable function of the pump can be achieved. Preferably the screw pump extends partially inside the drive shaft. With such a positioning of the screw pump, a very simple assembly can be realized.

Another aspect regards the power transmission for driving the second oil pump. In one embodiment the second oil pump is driven via the drive shaft. Preferably the second oil pump is driven via the drive shaft and a pair of pump gears. One of the pump gears can be an integral part of a component of the lower bevel gear set.

The gear pump ratio and/or the pump screw geometry can be changed to optimize the volume of oil exchanged and/or to achieve the desired direction of oil flow.

The gear ratio at the pair of pump gears can be chosen to optimize the circulating volume in the cooling oil circuit. Different gear ratios between the pair of pump gears will cause different rotation speeds of the pump. Hence, the optimum circulating oil volume can be achieved by an appropriate choice of the gear ratio.

The direction of the oil flow through the pump and the bore can be chosen to optimize the cooling of the oil. In other words, it can be decided if to let the oil go up or down through the bore in the drive shaft. This can be done for example by choosing the direction of rotation of the pump screw.

Overall, the presented solution is a very simple way to cool the oil from top to bottom or from bottom to top, in this type of marine drive units.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further and more particularly described in the following, by way of example only, and with reference to the accompanying figures.

FIG. 1 shows a marine drive unit according to the invention in a schematic drawing,

FIG. 2 shows a section of a further embodiment of a marine drive unit according to the invention, and

FIG. 3 shows a screw pump as used in the marine drive unit of FIG. 2.

DETAILED DESCRIPTION

A marine drive unit 1 as shown in FIG. 1 is driven by an engine 22, for example an internal combustion engine, which is located inside the hull 23 of a boat. The output shaft 24 of the engine 22 is coupled to an input shaft 9 of the marine drive unit 1. In this embodiment a joint shaft is coupled between the output shaft 24 and the input shaft 9. Input shaft 9 enters a upper housing 25 of an upper bevel gear set 2. The engine 22 and the upper housing 25 of the upper bevel gear set 2 are fastened to the hull 23 or to structural parts inside of the hull 23.

In the upper housing 25 there are a forward clutch 7 and a backward clutch 8 in the form of multi-disk-clutches provided to reverse the rotational direction of a drive shaft 4 with regard to the input shaft 9. The upper bevel gear set 2 connects the input shaft 9 to a vertically arranged drive shaft 4 and a lower bevel gear set 3 connects the drive shaft 4 to a horizontally arranged propeller shaft 26. A propeller 27 is rigidly fixed to the propeller shaft 26. The lower bevel gear set 3 and the propeller shaft 26 are supported in an underwater housing 14 which protrudes from the bottom of the hull 23 into the water. The underwater housing 14 can be rotated about a vertical rotation axis to adjust the steering direction of the propeller thrust and to steer the boat in the desired direction.

A first oil pump 5 is mounted in the upper housing 25 and driven by the input shaft 9. The first oil pump 5 delivers oil to the upper bevel gear set 2 for cooling and lubrication. Said first oil pump 5 supplies pressure for the hydraulic operation of the forward/reverse-clutches 7 and 8 which are provided to reverse the rotational direction of the drive shaft 4 with regard to the input shaft 9. Said first oil pump 5 sucks oil from an oil reservoir 11 inside the underwater housing 14.

Additionally, a second oil pump 6 is arranged at the lower end 10 of the drive shaft 4 to suck oil from the upper part of said oil reservoir 11 through a bore 12 inside the drive shaft 4 and to pump the oil into the lower part of the underwater housing 14. Thus, a cooling oil circuit is provided additionally to the pressure oil circuit effected by the first oil pump 5. Both said oil circuits can be operated with the same oil. Both said oil circuits are using the same oil reservoir 11.

The drive shaft 4 comprises an upper shaft section 15 and a lower shaft section 16 which are coupled with each other by means of a sleeve 18. The sleeve 18 has got several second openings 17 around its circumference. The oil level 33 in the underwater housing 14 is higher than the second openings 17 in the sleeve 18, so that oil can flow into the sleeve 18 and through a bore 12 in the lower shaft section 16 to the second oil pump 6 at the lower end 10 of the drive shaft 4.

FIG. 2 shows a sectional view of the lower part of another embodiment of a marine drive unit. The same components of the marine drive unit in FIG. 2 are indicated with the same referrals as in FIG. 1. The main difference of FIG. 2 are the two contra-rotating propellers 27 and 28 instead of the single propeller in FIG. 1. In this case the lower bevel gear set 3 comprises one driving bevel gear and two driven bevel gears. A first driven bevel gear is coupled by a hollow propeller shaft 29 to the first propeller 27 and a second driven bevel gear is coupled by the inner propeller shaft 30 to the second propeller 28.

The underwater housing 14 is fixed to a hollow steering shaft 31 which is rotatably supported in the hull 23 with roller bearing 32, so that the underwater housing 14 together with the propeller shafts 29 and 30 is rotatable about a vertical rotational axis 34.

A lower shaft section 16 of the drive shaft 4 is arranged with its greater part inside the underwater housing 14 of the marine drive unit 1. The inside space of the underwater housing 14 forms the oil reservoir 11. Therefor the underwater housing 14 is filled with oil. The oil reaches up into the steering shaft 31. The oil level 33 is higher than a sleeve 18, which couples the lower shaft section 16 to the upper shaft section 15 of the vertical drive shaft 4.

The second oil pump 6 is located at the lower end 10 of the drive shaft 4. The drive shaft 4 is coaxial to the rotational axis 34. The bore 12 extends from the upper end of the lower shaft section 16 to its lower end. The bore 12 is coaxial to the rotational axis 34. Several second openings 17 in the sleeve 18 are used as oil intakes into the bore 12, as the second oil pump 6 sucks oil from the oil reservoir 11 through the second openings 17 and the bore 12 to the lower end of the drive shaft 14. At the lower end 10 of the drive shaft 4 the second oil pump 6 pumps the oil through first openings 13 back into the oil reservoir 11. Thus, a cooling oil circuit is effected. There are two first openings 13 located near the lower end of a screw pump jacket 35.

In another embodiment of the invention, the direction of oil flow in the cooling oil circuit may be reversed. In such an embodiment the first openings 13 can be used as intakes for the oil. The oil will be pumped from the first openings 13 at the lower end 10 of the drive shaft 4 through the bore 12 upwards to second openings 17 in the drive shaft 4 and back into the oil reservoir 11.

The second oil pump 6 is shown in further detail in FIG. 3. The second oil pump 6 is a screw type pump. A pump screw 19 is arranged in a pump jacket 35 which can be fastened to the lower end 10 of the drive shaft 4. This way, the pump jacket 35 will rotate together with the drive shaft 4. The pump screw 19 will rotate with a different speed, depending on the gear ratio of a pair of pump gears 20 and 21, which drive the pump screw 19 as described below. An outer cylindrical surface of the pump screw 19 is dimensioned to fit into an inner cylindrical surface of the screw pump jacket 35. A collar 38 is arranged at the outside of the pump jacket 35. The collar 38 comprises screw holes 39, 40 for fastening the pump jacket 35 to the lower end 10 of the drive shaft 4.

The pump jacket 35 with the pump screw 19 extends partially inside the drive shaft 4 at its lower end 10. A cover 36 is fixed to the upper end of the pump jacket 35. Several orifices 37 in the cover 36 connect the inner space of the pump jacket 35 to the bore 2. A driving stud 41 of the pump screw 19 protrudes from the lower end of the pump jacket 35. A driven pump gear 21 is fixed to the driving stud 41. The driven pump gear 21 meshes with a driving pump gear 20. The driving pump gear 20 is manufactured together with a bevel gear wheel of the lower bevel gear set 3 from one piece. The pair of pump gears 20 and 21 can be modified to change the gear ratio. Thereby optimizing the volume of oil exchanged in the cooling oil circuit.

REFERENCES

- 1 marine drive unit
- 2 upper bevel gear set
- 3 lower bevel gear set
- 4 drive shaft
- 5 first oil pump
- 6 second oil pump
- 7 clutch
- 8 clutch
- 9 input shaft
- 10 lower end
- 11 oil reservoir
- 12 bore
- 13 first opening
- 14 underwater housing
- 15 upper shaft section
- 16 lower shaft section
- 17 second opening
- 18 sleeve
- 19 pump screw
- 20 pump gear
- 21 pump gear
- 22 engine
- 23 hull
- 24 output shaft
- 25 upper housing
- 26 propeller shaft
- 27 propeller
- 28 propeller
- 29 hollow propeller shaft
- 30 inner propeller shaft
- 31 steering shaft
- 32 roller bearing
- 33 oil level
- 34 rotational axis
- 35 pump jacket
- 36 cover
- 37 orifice
- 38 collar
- 39 screw hole
- 40 screw hole
- 41 driving stud