Iveco Marine Diesel Engines, Руководство по установке

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MARCH 2004 DRIVE
3.47
MARINE ENGINES INSTALLATION
The use of the inverter-reducer unit sets the correct drive ratio between the engine and the propeller
and makes it possible to reverse the boat travelling direction.
The main types of inverter-reducer units are equipped with oil bath multi-disc clutches actuated by the
oil under pressure and cooled down by an oil-sea water heat exchanger fitted on the inverter or the
engine. For low powers, mechanically-operated reducers-inverters are used. The reduction ratio can
range between 1:1 and 6:1 according to the type and size of the inverter and its use.
The reducer output shaft can be coaxial to the input shaft or offset downwards; there are also versions
fitted with the output shaft in angled position which makes it possible to substantially reduce or reset
the assembly tilt of the engine, thus making it easier to install it on the hull.
NOTE
Inverters different from those proposed by IVECO shall receive prior approval.
It is extremely important to insert the damper snap joint in the connection between the engine fly-
wheel and the inverter input shaft, in order to prevent twisting and overloading the engine shaft end.
For this reason, the joints must not only have the suitable flexibility and torsion dampening capability,
but also the right axial adaptability and the choice must take into consideration the boat purpose.
If at the shipyard it is decided to insert a snap joint between the engine and the propeller supporting
axis, it must be accurately selected to ensure the transmittability of the power, torque and the axial
thrust which is to be transmitted by the axis-propeller. If a separate thrust bearing is used, the snap joint
to be inserted shall not bear the thrust and is to be inserted between the reducer and thrust bearing.
One of the shipyard tasks is to choose the best solution.
Choice
The choice of the inverter-reducer depends on the type of boat and the performances required. This
choice is usually made in agreement with the designer and the boat builder since the type of hull, the
scope and the required performances influence the choice of the propeller.
The structure of the boat is fundamental for the position of the engine and the axis line just as the
choice of the inverter flanged on the engine or separated.
The performances required to the inverter, obviously compatible with the above mentioned ones in
relation to the engine and its use on pleasure boats, for light commercial service or continuous service
depend on the engine power, the type of propeller to be installed and the layout of the engine room.
The basic factors to make the right choice are the power/rpm ratio, i.e. the torque transmitted and the
maximum operating speed equal to that reachable by the engine. As the reduction ratios are available
in discrete succession, but not continuous, it is necessary to evaluate correctly the sizes in order to
match engine, inverter-reducer, user.
For the choice of the reducer-inverter it is also important to consider the movement reversal alterna-
tion which, if very close, requires the use specific components.
For heavy duty applications you are suggested to check the suitability of the thrust bearing installed by
factory on the inverter; if necessary, as in the event of high reduction ratios, insert an additional thrust
bearing to be dimensioned at the shipyard.
The boat thrust bearing is necessary to prevent transmitting vibrations to the boat, when the engine is
fitted with flexible supports and the propeller axis is not flexible enough to follow its movements
Efficiency
The mechanical efficiency of the reducer-inverter is an index of how much the output power is lower
than the one supplied to it; the efficiency varies according to the type of project and building, in par-
ticular if carried out by means of ordinary or epicycloid gearing.
The value can vary from 0.89 for the solution with epicycloid gearing at high reduction ratio and high
rotation speed, to 0.96 - 0.97 of a direct drive system with straight or helicoid teeth extremely refined
and with low rotation speed.
The presence of auxiliary power takeoffs on the reducer/multiplier reduces the power transmittable by
the output shaft according to what is given to the power takeoffs.
3.3 INVERTER-REDUCER