Boat propeller transmission The present invention relates to a boat propeller transmission comprising an input shaft intended to be connected to an output shaft from a drive installation, an inter- mediate shaft driven by said input shaft via a first bevel gear set, at least one pro- peller shaft driven by said intermediate shaft via a second bevel gear set, a reversing mechanism for reversing the rotational direction of the propeller shaft relative to said input shaft, and a gear set, providing at least two different gear speeds in the same direction between the input shaft and the propeller shaft.

Boat propeller transmissions, e. g. in propeller drives of the type which are steerably and tiltably mounted on the outside of a boat transom and which are drivably coupled to an inboard engine, usually have only a reversing transmission for reversing the rotational direction of the propeller shaft. Recently, however, two- speed propeller drives have been developed primarily for achieving more rapid acceleration so that the boat will more rapidly reach the planing position for better fuel economy. In boats with turbo-charged diesel engines, the poor charging capa- city of the turbo unit at low engine rpm has been compensated with a displacement compressor, which is mechanically driven by the engine and which is coupled in series with the turbo compressor and supercharges in the low rpm range of the engine, but which is disconnected as soon as the charging capacity of the turbo compressor exceeds the charging capacity of the displacement compressor. In this manner, rapid acceleration is achieved, so that the planing position can be rapidly reached. With a two-speed propeller drive unit with a low gear and a direct gear, the engine in low gear reached earlier the rpm at which the turbo compressor charges efficiently, which provides more rapid acceleration and earlier planing over a single speed transmission. With a two-speed drive unit it is possible in a boat with an engine only turbo-charged, to achieve approximately the same performance as a boat with a single speed drive unit and an engine with both a turbo compressor and a displacement compressor. The cost of manufacturing a propeller drive unit with an

extra gear speed is, however, significantly lower than the extra cost for the displace- ment compressor installation.

It is previously known to place a two-speed transmission on the inside of the boat transom between the output shaft on an inboard engine and the input shaft to the outboard drive unit. A disadvantage of such an installation is, however, firstly, that the engine must be moved forward, which results in poorer weight distribution and poorer high-speed performance, and, secondly, that one or the other type of trans- mission must be selected at the stage of designing the boat hull. It is thus not possible to have a standard hull with an engine bed, providing a free choice of a one-speed or a two-speed transmission.

In another known embodiment of a two-speed boat propeller transmission, the gear set with two-gear speeds is built into the drive housing on the outside of the transom. The input shaft of the transmission thus forms the input shaft to the gear unit, the output shaft of which forms the input shaft of the first bevel gear set.

This does avoid the disadvantages of the two-speed transmission placed inboard described above but, on the other hand, other disadvantages arise. Firstly, the propeller housing of the drive unit will be placed further out from the transom, which is disadvantageous with regard to the direction of the water flow, in which the propeller works, and, secondly, the tilt radius of the drive unit will be greater, thus limiting the trim and tilt angle of the drive unit.

The purpose of the present invention is to achieve a boat propeller transmission of the type described by way of introduction, by which the disadvantages of the two above described known transmissions are avoided.

This is achieved according to the invention by virtue of the fact that the gear unit is arranged between the bevel gear sets.

Thus, placement of neither the engine, nor the drive unit, relative to the transom is affected by whether a two-speed drive installation instead of a one-speed is installed in a boat.

The invention will be described in more detail below with reference to an example shown in the accompanying drawing, where Fig. 1 shows an upper longitudinal section, and Fig. 2 shows a lower longitudinal section through one embodiment of a boat propeller transmission according to the invention.

The transmission shown in the figures is of the type which, in a single-speed version, is used in steerable and tiltable outboard drives. The transmission shown is used in an outboard drive of the type commercially available under the trademark Aquamatic. The transmission has an input shaft 1, the outer end of which is joined to a universal knuckle intended to be drivably coupled to the output shaft from an engine. At its inner end, the axle is solidly joined to a bevel gear 3 engaging two bevel gears 4a and 4b, which are freely rotatably mounted on an intermediate shaft 5, mounted perpendicularly to the input shaft 1. The gears 4a and 4b can be alter- natingly locked to the intermediate shaft 5 with the aid of individual clutches 6 and 7 for driving the intermediate shaft 5 in one direction or the other. These can be hydraulically operated, multi-disc wet-disc clutches.

The lower end of the intermediate shaft 5 is non-rotatably joined to a ring gear 8 in a planetary gear set, generally designated 9. The ring gear engages planet gears 10, which are mounted on a planet gear carrier 11, which is joined to an output shaft 12 from the planetary gear set 9. The planet gears can engage a sun gear 13 made integral with a sleeve 14, through which the output shaft 12 extends. The sleeve 14 is rotatably mounted on the shaft 12 and has an externally threaded portion 15, which engages an internal thread in a bore 16 in a conical clutch element 17 having an external conical frictional surface 18 facing a conical frictional surface 19 of a bore 20 in an end plate 21 of a stationary housing 22. The clutch element 17 forms

at the same time an operating piston, and the bore 20 forms a cylinder in which the piston is axially displaceable. The ring gear 8 is made integral with a bowl-shaped carrier 23 of discs 24 arranged alternatingly with discs 25 on the planet gear carrier 11. The carrier 23 also forms a cylinder 26 for a piston 27 by means of which the package of discs 25,26 can be pressed together to lock the ring gear 8 to the planet gear carrier 11.

The output shaft 12 is joined via splines 28 to an input shaft 29 leading to a bevel gear set formed of three bevel gears of which the gear 30 is joined to the shaft 29 while the gears 31 and 32 are joined to two concentric propeller shafts, thus driven counter-rotationally.

In the position shown in Fig. 2 of the components, i. e. with the clutch 25,26 dis- engaged and the clutch element 17 and thus also the sun gear 13 locked against rotation, the low gear speed of the planetary gear set is engaged, i. e. the planet gear carrier 11 and the output shaft 12 rotate at a lower rotational speed than the inter- mediate shaft and the ring gear 8. Sufficiently high friction between the frictional surfaces 18 and 19 for locking the sun gear 13 is thus achieved by virtue of the fact that the thread 15 is so selected in relation to the reactive torque direction against the sun gear 13 when driving forwards that the conical element is affected by a downwardly directed force so that the frictional surfaces 18,19 are pressed against each other.

In a boat with a turbo-charged diesel engine, with low gear engaged, the rpm at which the charging capacity of the turbo compressor exceeds the capacity of a mechanically driven displacement compressor is rapidly reached. When this rpm has been reached, the higher gear speed (direct drive) is engaged. Shifting is effected by hydraulic fluid under pressure being conducted to an inlet 33 in the planetary gear housing 22. Via channels 34,35 and 36, the fluid is conducted to the cylinder chamber 26 behind the piston 27 and to a cylinder chamber 37 between the clutch element 17 and the housing end plate 21. From the channel 36, the fluid

flows in between the clutch element and the housing end plate by virtue of the fact that the frictional surfaces 18,19 are profiled so as to provide a certain amount of leakage therebetween. The oil pressure in the cylinder chamber 37 lifts the clutch element 17 so that the sun gear 13 is disengaged from the housing end plate 21. At the same time the oil pressure in the cylinder chamber 26, via the piston 27, presses the package of discs 24,25 together so that the entire planetary gear unit is locked together as a unit and forms a direct drive connection between the intermediate shaft 5 and the output shaft 12.