Abstract:
The multi-speed boat transmission for propulsion systems having a basic transmission for transmitting the motor power to a fixed propeller or water jet has, in addition to a preferably single-speed basic transmission ( 2 ), a separate front-mounted transmission ( 1 ) for flange-mounting to the basic transmission ( 2 ) and stepping-up parts ( 7, 8, 12 ), the countershafts ( 5 ) being distributed around the periphery of the main shaft ( 10 ) of the basic transmission in a manner such that no additional forces act upon the main shaft ( 10 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a multi-speed boat transmission. 
     BACKGROUND OF THE INVENTION 
     In conventional,boat transmissions, a fixed propeller is driven by a motor via a transmission having a constant ratio. The consequence of this construction is that the propulsion system can be optimally coordinated only for one operating point. 
     However, there are often situations in which such constructions have an unfavorable effect: when, e.g. the propulsion system is designed for a final speed as high as possible, the motor is pressed relative to the rotational speed when the boat resistance is increased as a result of weather conditions, cargo, etc. whereby only one part of the total power of the motor is available. Besides, the acceleration properties are poor and the thermal load of the motor is high. This also results in the production of soot. 
     On the other hand, if the propulsion system is designed for an acceleration as high as possible or for driving with elevated resistance, the nominal rotational speed of the motor under normal conditions is achieved without delivering full power in the process. This has a negative effect on the final speed obtainable. 
     It thus becomes necessary to optimize the propulsion device so that it is adaptable to different conditions of operation whereby the motor can always work in an optimal rotational speed range. 
     To that end, a variable-pitch propeller has been proposed. But this solution mechanically requires much expenditure and, consequently, is expensive and unusual in yachts/speed boats. A variable-pitch propeller also has poor efficiency. 
     SUMMARY OF THE INVENTION 
     DE 196 24 913 A1 discloses a marine propeller system having one motor, one shifting mechanism and one programmable electronic control device with a shifting parameter matrix. The electronic control device monitors the motor load and the revolution rate and produces a control signal which controls the shifting operations. Since this system forms one unit, it is not possible to change over already existing transmissions of the conventional kind mentioned above. On the contrary, new transmissions must be developed according to those requirements. 
     DE 31 02 556 A1 discloses a two-step transmission for boat propeller systems in which a planetary transmission is used. This transmission has a direct gear with a 1:1 ratio shiftable by a friction clutch for the cruising drive, while for a drive at highest speed a high speed gear is provided which is formed by the planetary transmission and a hydraulic clutch, and gears up the rotational speed. 
     With this construction, it is not possible to implement any small speed ratio changes for the high-speed range: likewise a simple change of the ratio is not possible. Furthermore, losses occur in the highest speed range. 
     Therefore, the problem on which this invention is based is to make a power shiftable boat transmission available which, in combination with a fixed propeller or water jet, allows a variable adaptation to different operating conditions. 
     Accordingly, on an already existing basic transmission, it is proposed to flange mount a separate front-mounted transmission having at least two countershafts wherein the countershafts are distributed around the periphery of the main shaft of the basic transmission in a manner such that no additional forces act upon the main shaft. The front-mounted transmission can be flange mounted on different transmission designs of boat propelling families without having to develop entirely new transmissions, therefore, the possible uses are multiple. 
     In addition, the front-mounted transmission is modularly built so that it can be coordinated by adapting a few parts to different operating conditions without having to develop new transmissions. 
     Besides, the stepping-up parts are configured in such a way that, via a provided plug-in system, it is possible to prepare both a gear up and a gear down ratio, with identical parts, but by a different assembly. Moreover, by varying the number of individual stepping-up parts teeth, different ratio ranges can be implemented. Moreover, by varying the number of individual stepping-up parts teeth, different ratio ranges can be implemented. 
     All this requires only a small assembly expenditure wherein almost arbitrary ratios can be implemented and, in particular, small ratio changes are also possible, unlike in a planetary transmission. 
     The construction proposed is of reasonable cost, since in most cases only a different assembly of identical parts is needed. It also offers a high measure of flexibility in regard to different requirements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in detail with the aid of the drawings which show: 
     FIG. 1 a  is a power-rotational speed diagram of a conventional boat propeller designed for high final speed; 
     FIG. 1 b  is a power-rotational speed diagram of a conventional boat propeller designed for high acceleration; 
     FIG. 2 is a cross-sectional representation of the front-mounted transmission according to a first variant of the instant invention; 
     FIG. 3 is a cross-sectional representation of the front-mounted transmission according to a second variant of the instant invention; 
     FIG. 4 is a cross-sectional representation of the front-mounted transmission according to a third variant of the instant invention. 
     FIG. 1 a  makes clear the need to adapt a boat propulsion system to different operating conditions: 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     If the propulsion system has been laid out for the highest possible final speed, the optimal operating point A, at a correspondingly high motor rotational speed n, is in the proximity of the nominal rotational speed n_max, which, in turn, results in a high generated power P in the proximity of the maximum power P_max. Under great boat resistance resulting from weather conditions, cargo, etc., the motor is pressed relative to the rotational speed and the optimum operating point cannot be reached. The new operating point A′ stands out by the fact that only a part of the total power of the motor is available. Besides, the acceleration property is poor and the thermal load of the motor high. This also results in the production of soot. 
     FIG. 1 b  illustrates another typical unfavorable situation: in the case shown, the propulsion system is laid out for high acceleration or high boat resistance. Thereby under normal conditions, the motor reaches the nominal rotational speed n_max at the operating point B without generating the full power P_max. 
     According to FIG. 2, a front-mounted transmission is flange-mounted on a basic transmission  2 . The motor drives a shaft  3 . According to the invention, it is possible, via a clutch  4 , to completely shift directly to the basic transmission, the ratio amounting to 1:1 or alternatively to select one other ratio i by means of both countershafts  5 . The ratio is activated by means of one other clutch or of one free wheel unit  6 . By virtue of the free wheel unit, the load is mechanically taken up automatically. 
     By virtue of the construction described here as a front-mounted transmission with power distribution over two symmetrically opposite countershafts  5 , no added forces act upon the basic transmission  2 , since the supporting forces of the main shaft  10  have been removed. No changes of the housing or of the support are therefore needed. 
     Within the scope of this special advantageous embodiment of the instant invention, helical-cut teeth are provided for noise reasons. In this case, in order to keep the main shaft  10  free of additional forces, pressure cams  11  are provided which assist generating axial forces of the main shaft wheels. 
     Between the gear ring of the helical-cut toothing  12  of the countershafts  5  and the main shaft  10 , a flexible annular connecting element  8  is provided of which one end meshes with the gear ring and the other end is connected with the main shaft  10 , a flexible area being provided between the two ends. The flexible area preferably has a reduced wall thickness. 
     By adequate selection of the stepping-up parts  7  and  8 , an optional gradation of the gears is possible so that an optimal coordination between motor and transmission can be obtained: to implement one other ratio, only toothing parts  12  have to be exchanged. 
     In addition, the stepping-up parts of the inventive front-mounted transmission are designed so that it is possible to obtain a ratio  1 /i reciprocal with the initial ratio i via a provided plug-in system  9  by a different assemblage with identical parts. 
     This situation is shown in FIG.  3 : Due to the opposite orientation of the countershafts  5  and to an adequate assembly of the parts  7  and  8 , and of the clutch and free-wheel devices  4  and  7 , a ratio  1 /i is obtained. 
     To this end, the stepping-up parts  7 ,  8 , by means of a plug-in system  9 , can be plugged and fixed respectively on the shaft  3  driven by the motor and the main shaft  10  of the basic transmission  2 . 
     The selection of the power shift can also be implemented without free wheel by using two regulated multi-disc clutches  4 ,  4 ′. This is illustrated in FIG.  5 : via the multi-disc clutch  4 ′, it is possible to completely shift to the basic transmission while, via the clutch  4 , the power is distributed to the countershafts  5 . The ratio obtained by the reproduced construction can be changed without much expenditure: to this end, the stepping-up parts are differently mounted, as explained already, whereby it is possible to achieve a ratio reciprocal to the initial one. 
     Although a two-speed transmission has been described, multi-speed transmissions are also conceivable by means of the front-mounted construction of the transmission that has been described. The invention Is not confined to a multi-speed boat transmission which has a separate basic transmission. A housing can be provided which comprises all ratio steps including those of the basic transmission. Depending on the kind of propulsion or total ratio required, a basic transmission can be entirely omitted. For this purpose, only the shaft connections have to be adapted. FIG. 3 shows such a transmission. 
     REFERENCE NUMERALS 
       1  front-mounted transmission 
       2  basic transmission 
       3  shaft 
       4  clutch 
       5  countershaft 
       6  free wheel 
       7  stepping-up part 
       8  stepping-up part, flexible connecting element 
       9  plug-in system 
       10  main shaft 
       11  pressure cam 
       12  helical-cut toothing