Patent Description:
A typical conventional marine propulsion system comprises one or two drive trains, each with a diesel engine and a transmission with speed reduction gear steps interposed between the engine and the propeller. This type of propulsion, in which the propeller characteristics and a certain reduction ratio between the engine and the propeller are preset at the design stage, often includes a modulatable transmission clutch for operating at lower speeds than a nominal speed.

In recent years there is an increasing demand for marine hybrid drive units for environmental and efficiency reasons. With a marine hybrid drive unit a boat can be propelled solely by an electric motor without any local emissions especially in ecologically sensitive areas or in harbors and mooring areas. During certain operating phases it is also more efficient to propel a boat solely by the electric motor, for example if a boat shall be propelled with low speed in a trolling mode or in a no-wake zone. The combustion engine of the hybrid drive unit provides sufficient power for normal and high-speed cruising.

Different marine hybrid drive units comprising a combustion engine and an electric motor are already known from prior art. One example of a marine hybrid drive unit with a transmission has been disclosed in <CIT>. Said transmission comprising a transmission input shaft for accepting power into the transmission and a transmission output shaft for outputting power to a propeller. A first prime mover is selectively coupled to the transmission input shaft, whereas a second prime mover is permanently coupled to the transmission input shaft. A modulatable clutch assembly is operably coupled to the transmission input and output shafts such that the power and speed from the input shaft can be variably transferred to the output shaft.

In <CIT> a boat drive is described, comprising a first drive engine and an additional drive machine, which can be coupled to drive an output shaft. The boat drive further comprises a lubrication pump which is driven by a drive shaft.

<CIT> discloses a marine drive unit comprising an upper bevel gear set, a lower bevel gear set, and a pressure operated clutch. A first oil pump is arranged to supply oil to the upper bevel gear set and to supply pressure for a pressure operated clutch. A second oil pump is arranged to feed a cooling oil circuit.

The purpose of the present invention is to provide an improved marine hybrid drive unit with a modulatable clutch, which allows optimized cruising conditions especially in a trolling mode with a simple structural design.

This purpose is achieved by a marine hybrid drive unit according to claim <NUM> and by a method according to claim <NUM>.

Further embodiments are claimed in dependent claims. The present invention provides a marine hybrid drive unit comprising a drive shaft which is connected to a combustion engine, an electric motor and a transmission with an input shaft and an output shaft. The input shaft of the transmission can selectively be driven solely by the combustion engine, solely by the electric motor or by the combustion engine and the electric motor simultaneously.

The transmission further includes a modulatable transmission clutch to selectively connect the input shaft to the output shaft. A modulatable transmission clutch allows for a continuous adjustment of the difference between the rotational speeds of the input shaft and the output shaft. The modulatable transmission clutch can be a pressure actuated hydraulic clutch, preferably in form of a multi-disk-clutch. For actuating the modulatable transmission clutch the transmission further comprises an oil pump, which is driven by the input shaft. The oil pump providing the oil pressure for the actuation of the modulatable transmission clutch. Therefore the pressure side of the oil pump is connected to a pressure chamber of the modulatable transmission clutch. At least one pressure control valve can be arranged to modulate the oil pressure in the pressure chamber accordingly.

Said input shaft is permanently connected to the electric motor via at least one gear step. The gear step may comprise several spur gears which are configured to provide an appropriate gear ratio between the electric motor and the input shaft. A suitable gear ratio of the at least one gear step can be set to drive the input shaft and the oil pump in all operating modes with an appropriate speed to provide sufficient oil for the actuation of the modulatable transmission clutch. In order to supply sufficient oil pressure and oil volume to the modulatable transmission clutch, especially in a trolling mode, the oil pump needs to be driven with a certain minimum speed. Therefore, it is essential, that the gear ratio is set to a value, which ensures said minimum speed at the pump while the electric motor can be operated as long as required in a technically feasible speed range. Otherwise the marine hybrid drive unit would need a second oil pump for the actuation of the modulatable transmission clutch in the trolling mode.

A certain minimum rotation speed of the input shaft is necessary to ensure that a sufficient oil pressure for the modulation of the modulatable transmission clutch is built up by the oil pump, which is driven by the input shaft. In one embodiment a minimum rotation speed of around <NUM>-<NUM> rpm is required at the input shaft. Hence, the gear ratio must be adjusted to a minimum operation speed of the electric motor to enable such operation mode. The electric motor in this embodiment can be driven with a minimum operation speed in the range between <NUM> rpm and <NUM> rpm. For such an application the gear steps are designed to provide a transmission ratio preferably in the range between <NUM> and <NUM>. Such a transmission ratio has proven to be sufficient to provide for the minimum speed at the input shaft and the minimum oil pressure in all operating modes. The proposed transmission ratio between <NUM> and <NUM> has proven to deliver an optimum range in view of the efficiency of the electric motor in the electric propulsion mode and in a recharge mode. In the recharge mode, the electric motor can be used as a generator to recharge the batteries, while the input shaft is driven by the combustion engine.

There is a pressure actuated input clutch provided to connect and disconnect the drive shaft to the input shaft. The oil pump is arranged to provide oil for the actuation of the pressure actuated input clutch, as well as for the modulatable transmission clutch. The input clutch and the electric motor can be arranged inside a module housing of a hybrid module which is mounted in between the combustion engine and the transmission.

The transmission may comprise an oil lubrication system and said oil pump can be configured to supply oil to the oil lubrication system, as well. A correct lubrication in terms of oil flow rate and pressure can be achieved in such an oil lubrication system to ensure a continuous and reliable cooling and lubrication of the components in the transmission and in the hybrid module. In such an oil supply system there can be a separate low-pressure section for the oil lubrication system, while the oil supply to the pressure actuated input clutch and the modulatable transmission clutch is provided by a high-pressure sections. Oil can be supplied to the low-pressure section and the high-pressure section by only one oil pump.

That means, that the full functionality of the marine hybrid drive can be achieved with only one oil pump. Preferably the oil pump is an integral component of the transmission. No additional oil pump is required for one of said functions.

Another aspect of the invention is a method for driving such a marine hybrid drive unit in a trolling mode when the hybrid drive unit is driven solely by the electric motor. In this operation mode the oil pump provides the oil pressure for the actuation of the modulatable transmission clutch, and wherein the speed of the output shaft is continuously adjustable by means of the modulatable transmission clutch in a range between <NUM>% and <NUM>% of the speed of the input shaft. Especially a speed reduction ratio in the lower section of said range allows to drive the boat with low and very low speed. Such low speed can be required for docking maneuvers and in so-called no wake zones. A no-wake zone is a section of a waterway with a strict speed limit. When navigating through a no-wake zone, state and/or local regulations generally require that the captain observe the slowest-possible vessel speed to maintain steerage. There might be a certain speed limit of a maximum speed of <NUM> miles hour (<NUM>,<NUM>/h), per example. The goal is to minimize the wake created by boats passing through the zone.

The proposed marine hybrid drive unit and the method allow to operate a boat in the full range of operating modes and speeds without the need of an additional oil pump for the actuation of one of the pressure actuated clutches.

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

The marine hybrid drive unit <NUM> as shown in <FIG> can be mounted inside the hull of a boat. The marine hybrid drive unit <NUM> comprises a combustion engine <NUM> and an electric motor <NUM> for propelling the boat in different operation modes.

The marine hybrid drive unit <NUM> further comprises a transmission <NUM> with an input shaft <NUM> and an output shaft <NUM>. The input shaft <NUM> can selectively be driven by the combustion engine <NUM>, by the electric motor <NUM> or by the combustion engine <NUM> and the electric motor <NUM> simultaneously. The output shaft <NUM> in this embodiment being arranged with a downward angle with regard to the input shaft <NUM>. The output shaft <NUM> being connected to a propeller shaft of the boat either directly or via further transmitting elements.

The combustion engine <NUM> includes a crankshaft <NUM> which is connected to the drive shaft <NUM>. The connection between the crankshaft <NUM> and the drive shaft <NUM> may comprise a flywheel and/or torsional dampers which are not shown in the scheme of <FIG>. This embodiment includes a separate electric starter unit <NUM> for starting the combustion engine <NUM>. However, other embodiments can be configured without a separate electric starter unit <NUM>, as the combustion engine <NUM> might also be started by the electric motor <NUM> with the input clutch <NUM> being engaged.

Drive shaft <NUM> can be connected and disconnected to an input shaft <NUM> of the transmission <NUM> by means of a pressure actuated input clutch <NUM>. The drive shaft <NUM> and the input shaft <NUM> are arranged coaxial to each other. The drive shaft <NUM> is fastened to an input element <NUM> of the input clutch <NUM> whereas the input shaft <NUM> is fastened to an output element <NUM> of the input clutch <NUM>. The input clutch <NUM> in this embodiment is a multi-disk-friction-clutch with inner and outer friction disks. The input element <NUM> being designed as an inner disk carrier, whereas the output element <NUM> is designed as an outer disk carrier. The inner and outer friction plates are pressed against each other to provide for the required transmission of torque.

The input clutch <NUM> and the electric motor <NUM> are part of a hybrid module <NUM> which is mounted in between the combustion engine <NUM> and the transmission <NUM>. The electric motor <NUM> is mounted to a module housing <NUM> of the hybrid module <NUM> such, that a motor shaft <NUM> of the electric motor <NUM> is arranged in parallel to the input shaft <NUM>. The electric motor <NUM> is permanently connected to the input shaft <NUM> and to the output element <NUM> of the input clutch <NUM>.

The transmission <NUM> further includes a modulatable transmission clutch <NUM> to selectively connect the input shaft <NUM> to the output shaft <NUM>. The modulatable transmission clutch <NUM> is arranged inside a transmission housing <NUM>. The modulatable transmission clutch <NUM> is configured to control the speed of an output shaft <NUM>. The modulatable transmission clutch <NUM> is a hydraulically actuated multi-disk clutch. The modulatable transmission clutch <NUM> can be fully engaged, fully disengaged or it can be operated in slipping operation. The slipping operation of the modulatable transmission clutch <NUM> can be used for propelling the boat in a trolling mode with low speed. This way, the speed of the output shaft <NUM> can be adjusted continuously in a range between <NUM>% and <NUM>% with regard to the speed of the input shaft <NUM>. In the trolling mode the hybrid drive unit <NUM> can be driven solely by the electric motor <NUM>.

The transmission <NUM> comprises an oil pump <NUM>, which is driven by the input shaft <NUM> to provide oil to the oil lubrication system, for actuating the pressure actuated input clutch <NUM> and for actuating the modulatable transmission clutch <NUM>. The oil supply system includes the oil pump <NUM>, connecting ducts and/or pipes, valves and further hydraulic components to provide and to control an appropriate oil pressure for all mentioned purposes.

The input shaft <NUM> is permanently connected to the electric motor <NUM> via gear steps <NUM>, wherein a gear ratio of the gear steps <NUM> is set to drive the input shaft <NUM> with the oil pump <NUM> in all operating modes with a speed to provide sufficient oil pressure for the actuation of the modulatable transmission clutch <NUM>. The gear ratio of the gear steps <NUM> is in the range between <NUM> and <NUM>. The gear steps <NUM> are part of the hybrid module <NUM> and arranged inside the module housing <NUM>. The gear steps <NUM> comprise a first spur gear <NUM> which is fastened to the motor shaft <NUM>. The first spur gear <NUM> meshes with a second spur gear <NUM> which is supported in the module housing <NUM>. The second spur gear <NUM> further meshes with a toothing <NUM> which is an integral part of the output element <NUM> of the input clutch <NUM>. The pressure actuated input clutch <NUM> is also a part of the hybrid module <NUM>.

Claim 1:
Marine hybrid drive unit (<NUM>) comprising
a drive shaft (<NUM>) which is connected to a combustion engine (<NUM>),
an electric motor (<NUM>),
a transmission (<NUM>) with an input shaft (<NUM>) and an output shaft (<NUM>),
wherein the input shaft (<NUM>) can selectively be driven solely by the combustion engine (<NUM>), solely by the electric motor (<NUM>), or by the combustion engine (<NUM>) and the electric motor (<NUM>) simultaneously,
wherein the input shaft (<NUM>) is permanently connected to the electric motor (<NUM>) via at least one gear step (<NUM>),
a modulatable transmission clutch (<NUM>) to selectively connect the input shaft (<NUM>) to the output shaft (<NUM>),
a pressure actuated input clutch (<NUM>) which is provided to connect and disconnect the drive shaft (<NUM>) to or from the input shaft (<NUM>),
characterized in, that the transmission (<NUM>) further comprises an oil pump (<NUM>), which is driven by the input shaft (<NUM>) to provide oil pressure for actuating the modulatable transmission clutch (<NUM>), and that the oil pump (<NUM>) is arranged to provide oil for the actuation of the pressure actuated input clutch (<NUM>).