METHOD FOR STARTING A COMBUSTION ENGINE IN A MARINE HYBRID DRIVE UNIT

A method is disclosed for starting a combustion engine in a marine hybrid drive unit where the marine hybrid drive unit includes the combustion engine and an electric drive motor. The combustion engine has an electric starter unit, and the electric drive motor is permanently connected to the driven shaft. A driven shaft of the marine hybrid drive unit can be driven in a combustion engine mode solely by the combustion engine, in an electric propulsion mode solely by the electric drive motor, and in a combined mode by the combustion engine and the electric drive motor. The method includes starting the electric motor and starting the combustion engine by the electric starter unit. Also disclosed is a marine hybrid drive unit comprising a control unit configured to execute the method.

RELATED APPLICATIONS

This application claims the benefit of and right of priority under 35 U.S.C. § 119 to European Patent Application no. 23180297.6, filed on 20 Jun. 2023, the contents of which are incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present invention relates to a method for starting a combustion engine in a marine hybrid drive unit.

BACKGROUND

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 drive 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 drive motor, for example if a boat shall be propelled with low speed in a trolling mode or in a no-wake area. Whereas the combustion engine provides sufficient power for normal and high-speed cruising.

Different marine hybrid drive units comprising a combustion engine and an electric drive motor to propel a water vehicle are already known from prior art. One example of a marine drive hybrid drive unit has been disclosed in US 2009/0209146 A1. This document describes a hybrid module for installation between an internal combustion engine and a transmission of a watercraft. The combustion engine and an electric drive motor of the hybrid module may be selectively used to propel a watercraft. Different embodiments of such a hybrid module and different start and driving modes are disclosed with this document. One embodiment is described with a separate starter unit being required to start the combustion engine.

SUMMARY

The purpose of the present invention is to provide an improved method for starting a combustion engine in a marine hybrid drive unit and a marine hybrid drive unit comprising a control unit, which is arranged to implement such a method.

This purpose is achieved by a method for starting a combustion engine in a marine hybrid drive unit, and a marine hybrid drive unit as disclosed herein. Further embodiments will be apparent in light of the present disclosure.

The present invention provides a method for starting a combustion engine in a marine hybrid drive unit, wherein the marine hybrid drive unit comprises the combustion engine and an electric drive motor. The combustion engine comprises an electric starter unit containing a further electric motor.

A driven shaft of the marine hybrid drive unit can be driven in different modes. It may be driven solely by the combustion engine in a combustion engine mode. In an electric propulsion mode, the driven shaft may solely be driven by the electric drive motor. In this electric propulsion mode, the boat can be propelled at zero noise and zero emissions, especially during low-speed cruising and docking. In a combined mode the driven shaft may be driven by the combustion engine and the electric drive motor simultaneously. The electric drive motor is permanently connected to the driven shaft. This way, the electric drive motor can be used as a generator to recharge the batteries, while the driven shaft is driven by the combustion engine in the combustion engine mode.

The combustion engine of such a marine hybrid drive unit can be started according to the proposed method comprising the steps:a) starting the electric drive motor,b) starting the combustion engine by the electric starter unit.

Starting the electric drive motor before starting the combustion engine excludes the inertia from the elements of the electric drive motor and all components being connected to it, during the subsequent starting of the combustion engine. This way an overload of the electric starter unit of the combustion engine is avoided, even so the electric starter unit had been designed to start a conventional combustion engine without any additional hybrid components. This means, that an existing conventional marine drive unit without electric driving motor can be modified by a hybrid module comprising the electric drive motor without modifying the combustion engine with its electric starter unit. Said hybrid module may include its own housing to enclose at least some components of the electric drive train. The electric drive motor can either be enclosed in said housing or it can be located outside the housing.

One embodiment of such a marine hybrid drive unit comprises a freewheel unit, wherein an input part of the freewheel unit is connected to a crankshaft of the combustion engine and wherein an output part of the freewheel unit is connected to the electric drive motor and to the driven shaft. The freewheel unit allows different rotational speed between the crankshaft of the combustion engine and the driven shaft. A freewheel or overrunning unit is a cheap and simple solution compared to an active clutch which requires additional efforts for the actuation and control of the active clutch. The freewheel unit can be a part of the hybrid module.

However, in other embodiments and for other applications an active clutch can be used. This means that the combustion engine can be disconnected and connected to the driven shaft by means of a pressure actuated input clutch. In such an embodiment the proposed method shall include a step to close the pressure actuated clutch before starting the combustion engine. The oil pressure for actuating the input clutch can be provided by an oil pump, which is driven by the electric drive motor via the driven shaft. Hence, the pressure actuated input clutch can be actuated as soon as the electric drive motor has been started and the driven shaft is rotating with a certain speed. The pressure actuated input clutch can be closed after starting the electric drive motor and before starting the combustion engine. In an embodiment that comprises at least one gear step between the electric drive motor and the driven shaft, the gear ratio of the at least one gear step can be optimized to build up an appropriate oil flow rate and oil pressure provided by the oil pump. This way, the use of an auxiliary electric pump is not necessary during the starting procedure.

The marine hybrid drive unit may be switched in the combustion engine mode when the combustion engine has reached a preset engine speed. Preferably the preset engine speed is set to a value in a range between 600 rpm and 800 rpm. This speed shall be the idling speed of the corresponding combustion engine, which is also appropriate to drive the electric drive motor in a recharge mode.

The invention includes a marine hybrid drive unit comprising a control unit, which is arranged to implement a method as described above. The electric drive motor preferably is part of a hybrid module comprising at least one gear step between the electric drive motor and the driven shaft. The at least one gear step is used to apply an optimized gear ratio between the electric drive motor and the driven shaft. One target of the optimized gear ratio is to maximize the efficiency of the electric drive motor either in the electric propulsion mode or in the recharge mode. For that purposes the gear ratio of the at least one gear step preferably is set to a value in the range between 2 and 3.

The driven shaft can be an input shaft of a gearbox, so that the hybrid module can be installed between the combustion engine and the gearbox. In this embodiment, the mentioned oil pump can be an integral part of the gearbox and it can be driven by said input shaft. Transmission elements are arranged in the gearbox to transfer the rotational speed of the input shaft to a required speed of an output shaft which is connected to a propeller shaft of the boat. Further transmission elements like one or more clutches can be arranged in the gearbox to connect or disconnect the input shaft from the output shaft and/or to change the direction of rotation between the input shaft and the output shaft.

DETAILED DESCRIPTION

A marine hybrid drive unit100as shown inFIG.1can be mounted inside the hull of a boat. The marine hybrid drive unit100comprises a combustion engine1and an electric drive motor2for propelling the boat in different operation modes. The marine hybrid drive unit100can be driven in a combustion engine mode solely by the combustion engine1, in an electric propulsion mode solely by the electric drive motor2. In a combined mode the marine hybrid drive unit100can be driven simultaneously by the combustion engine1and the electric drive motor2.

The combustion engine1includes an electric starter unit8and a crankshaft9. The crankshaft9can be connected to a driven shaft4by means of a pressure actuated input clutch5. The crankshaft9and the driven shaft4are arranged coaxial to each other. The crankshaft9is fastened to an input element12of the input clutch5whereas the driven shaft4is fastened to an output element13of the input clutch5. The input clutch5in this embodiment is a multi-plate-friction-clutch with inner and outer friction plates. The input element12being designed as an inner disk carrier, whereas the output element13is designed as an outer disk carrier. The input clutch5is configured to be pressure actuated by means of an appropriate oil supply system.

An oil pump6is provided to supply sufficient oil pressure for actuating the input clutch5. The oil pump6is driven by the driven shaft4. In this embodiment the driven shaft4is the input shaft of a gearbox14. The gearbox14comprises a transmission clutch15which is configured to control the speed of an output shaft16of the gearbox14. The transmission clutch15is a hydraulically actuated multi-disc clutch. The transmission clutch15can be fully engaged, fully disengaged or it can be operated in a slipping mode for propelling the boat with low speed. In the slipping mode a slip rate of the transmission clutch15can be adjusted by controlling the oil pressure in the hydraulic actuation system of the transmission clutch15. The oil pressure in said hydraulic actuation system is provided by the oil pump6.

The input clutch5and the electric drive motor2are part of a hybrid module10which is mounted in between the combustion engine1and a gearbox14. The electric motor2is mounted to a housing11of the hybrid module10such, that a motor shaft3of the electric drive motor2is arranged in parallel to the driven shaft4. The electric drive motor2is permanently connected to the driven shaft4and to the output element13of the input clutch5.

The hybrid module10further includes gear steps7between the electric drive motor2and the driven shaft4. The gear steps7in this embodiment comprises a first spur gear17which is fastened to the motor shaft3. The first spur gear17meshes with a second spur gear18. The second spur gear18further meshes with a toothing19which is an integral part of the output element13of the input clutch5. The gear steps7are designed to provide a transmission ratio in the range between 2 and 3, as this has proven to be the optimum range in view of the efficiency of the electric drive motor2in the electric propulsion mode and in the recharge mode. The pressure actuated input clutch5is also a part of the hybrid module10.

A control unit101of the marine hybrid drive unit100is configured to execute the proposed method for starting the combustion engine1. The control unit101is further configured to control the engagement of the pressure actuated transmission clutch15in a way to control the speed of the output shaft16and the speed of a propeller which is connected to the output shaft16. For these purposes the control unit101contains electronic and hydraulic components like valves for the control of oil flow and oil pressure. The control unit101further includes interfaces to be connected to a control unit of the combustion engine1and/or other control units of the boat. The control unit101may additionally control oil pressure and oil flow for the lubrication of elements in the gearbox14and in the hybrid module10.

An alternative embodiment of a marine hybrid drive unit200as shown inFIG.2differs from the embodiment ofFIG.1in the type of the input clutch23, which is part of the hybrid module20. The input clutch23in this alternative embodiment is designed as a freewheel unit with an input element21and an output element22. The crankshaft9is fastened to the input element21whereas the driven shaft4is fastened to an output element22of the input clutch23. Hence the input clutch23of this embodiment is a passive clutch, which does not need an active actuation. This type of input clutch23allows the output element22and the driven shaft4to rotate faster than the input element21, which is usually the case in the electric propulsion mode. The control unit201in this embodiment does not need to control the input clutch23. The control unit201in this embodiment controls the oil pressure for lubricating the elements in the gearbox14and in the hybrid module20and the oil pressure for the actuation of the transmission clutch15.

FIG.3shows schematically the steps of the proposed method. In a first step S1the electric drive motor2is started. In the following step S2a pressure actuated input clutch5is closed after starting the electric drive motor2. The combustion engine1is connected to the driven shaft4by applying pressure to the pressure actuated input clutch5, wherein the oil pressure is provided by an oil pump6, which is driven by the driven shaft4. In step S3the combustion engine is started by the electric starter unit8, wherein the electric starter unit8has to overcome only the inertia of the elements from the combustion engine1to the input element12,21of the input clutch5, because all further elements of the drive train are already driven by the electric drive motor2. Step S2and step S3can be activated almost simultaneously or with a very short time lag, in order to avoid an overload of the electric drive motor2during the start of the combustion engine1. A recharge mode to operate the electric drive motor2as a generator can be activated in step S4as soon as the combustion engine1is running with a preset speed.

REFERENCES