Patent Publication Number: US-11383811-B2

Title: Method for controlling the propulsion of a ship

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/EP2018/068248, filed Jul. 5, 2018, which claims priority from Swedish Patent Application No. 1750935-7, filed Jul. 14, 2017, the disclosures of which are incorporated by reference herein. 
     TECHNICAL FIELD 
     The present invention relates to a method for controlling the propulsion of a ship. Moreover, the present invention relates to a computer program, a computer readable medium, a control unit and a ship. 
     BACKGROUND 
     A controllable pitch ship propeller is designed such that the angle of attack of the blade can be continuously varied. In this manner, the torque of the main engine may be varied. A controllable pitch propeller is common for medium sized ships (50-150 m l.b.p.) with medium to high requirements on maneuverability. 
     Although a ship with a controllable pitch propeller can be maneuvered with an appropriated flexibility, contemporary ships often consume more fuel than necessary, for instance due to inappropriate operation settings of the ship&#39;s engine or the controllable pitch propeller. 
     SUMMARY 
     In view of the above, according to a first aspect of the present invention, an object of the present invention is to provide a method for controlling the propulsion of a ship wherein the engine of the ship is operated in appropriate operating conditions. 
     The above aspect is obtained by a method according to claim  1 . 
     As such, the first aspect of the present invention relates to a method for controlling the propulsion of a ship. The ship comprises an engine and a controllable pitch propeller, wherein torque and engine speed are adjusted to correspond to an output set point value. The adjustment is such that the ship is operated in an operating condition with an engine speed of the engine and a propeller pitch of the controllable pitch propeller such that the fuel consumption of the ship is brought and/or held within a desired fuel consumption range. 
     According to the first aspect of the present invention, the method comprises:
         determining a NO value indicative of a NO content in the exhaust gas produced by the engine and   reducing the torque of the engine upon detection that the NO x  value exceeds a NO x  threshold value.       

     As such, by virtue of the above method, a control of the propulsion of a ship is proposed wherein the engine is operated with an appropriate fuel consumption and wherein the NO x  content also can be kept appropriately low. Thus, the above method implies an operating condition of the ship which is less harmful to the environment as compared to previously used operating conditions. Moreover, keeping the fuel consumption within the desired fuel consumption range implies cost reductions. 
     As used herein the term “NO x  content” relates to the total content of nitrogen monoxide NO and nitrogen dioxide NO 2 . It should however be noted that this term is also intended to mean the content of nitrogen monoxide or nitrogen dioxide if measured separately. 
     By virtue of the above method, an actual NO x  content in the exhaust gas produced by the engine may be taken into account when controlling the propulsion of the ship. Thus, instead of determining constraints on e.g. the torque from simulations and/or tests in a test environment in order to avoid high NO x  content levels when operating the ship&#39;s engine, the above method implies that the actual NO x  content may be taken into account. Purely by way of example, the amount of NO x  produced by the engine of a ship may vary throughout the life of the engine, for instance due to aging and/or wear, and such variations may be automatically accounted for in the above method. 
     Optionally, the ship comprises an exhaust gas system adapted to guide exhaust gases from the engine, the exhaust gas system comprising a NO x  reduction assembly. 
     Optionally, the method comprises determining the NO x  value by evaluating exhaust gas between, as seen in an intended direction of exhaust gas flow, the engine and the NO x  reduction assembly in the exhaust gas system. Measuring the NO x  content between the engine and the NO x  reduction assembly implies that the NO x  content measured is the NO x  content in the exhaust gases produced by the engine. As such, the above method implies a rapid and stable control of the engine since the control is for instance not dependent on any changes of the capacity, for instance due to aging, of the NO x  reduction assembly. 
     Optionally, the method comprises determining the NO value by evaluating exhaust gas downstream, as seen in an intended direction of exhaust gas flow, of the NO x  reduction assembly in the exhaust gas system. Measuring the NO x  content downstream of the NO x  reduction assembly implies that the NO x  content measured is the NO x  content in the exhaust gas that will enter the environment ambient of the ship. As such, the above method implies that the engine can be controlled such that the NO x  content does not exceed predetermined emission levels which for instance may be legal emission levels. 
     Optionally, the method comprises determining a geographical location of the ship and determining the NO x  threshold value on the basis of the thus determined geographical location. Different geographical areas of the world may be associated with different allowable emission levels. As such, the above method, being adapted to adjust the NO x  threshold value in dependence on the determined geographical location, implies that such different allowable emission levels may be taken into account when setting the NO x  threshold value. This in turn implies an appropriate operation of the engine with appropriate NO x  emission levels as well as an appropriate fuel consumption. 
     Optionally, the engine speed of the engine is increased upon detection that the NO x  value exceeds the NO x  threshold value. The speed increase implies that the ship may produce the requisite power, as indicated by the output set point value, whilst still producing exhaust gases with a NO x  content lower than or equal to the NO x  threshold value. 
     A second aspect of the present invention relates to a method for controlling the propulsion of a ship. The ship comprises an engine and a controllable pitch propeller. The engine comprises least one cylinder. The torque and engine speed are adjusted to correspond to an output set point value, wherein the adjustment is such that the ship is operated in an operating condition with an engine speed of the engine and a propeller pitch of the controllable pitch propeller such that the fuel consumption of the ship is brought and/or held within a desired fuel consumption range. 
     According to the second aspect of the present invention, the method comprises:
         determining a top pressure value indicative of a top pressure in the at least one cylinder and   reducing the torque of the engine upon detection that the top pressure value exceeds a top pressure threshold value.       

     Excessive top pressures may be harmful to the engine. As such, by virtue of the above method according to the second aspect of the present invention, the risk of damaging the engine may be kept appropriately low. 
     Optionally, the engine speed of the engine is increased upon detection that the top pressure value exceeds the top pressure threshold value. 
     Optionally, for the first and/or second aspects of the present invention, the feature of reducing the torque of the engine comprises reducing the propeller pitch of the controllable pitch propeller. 
     A third aspect of the present invention relates to a computer program comprising program code means for performing the steps of any one of the first or second aspects of the present invention when the program is run on a computer. 
     A fourth aspect of the present invention relates to a computer readable medium carrying a computer program comprising program code means for performing the steps of any one of the first or second aspects of the present invention when the program product is run on a computer. 
     A fifth aspect of the present invention relates to a control unit for controlling the propulsion of a ship. The ship comprises an engine and a controllable pitch propeller, wherein the control unit is adapted to receive a signal indicative of an output set point value. The control unit is also adapted to issue control signals to control the engine speed of the engine and the propeller pitch of the controllable pitch propeller in response to the output set point value. The control signals are determined such that the ship is operated in an operating condition, corresponding to the output set point value, with an engine speed of the engine and a propeller pitch of the controllable pitch propeller such that the fuel consumption of the ship is brought and/or held within a desired fuel consumption range. 
     According to the fifth aspect of the present invention, the control unit is adapted to:
         receive a NO x  signal with a NO x  value indicative of a NO x  content in exhaust gas produced by the engine and to   issue a control signal to reduce the torque of the engine upon detection that the NO x  value exceeds a NO x  threshold value.       

     Optionally, the ship comprises an exhaust gas system adapted to guide exhaust gas from the engine, the exhaust gas system comprises a NO x  reduction assembly. 
     Optionally, the control unit is adapted to receive a signal with a NO x  value indicative of the NO x  content in the exhaust gas from a NO x  sensor being located in a position between, as seen in an intended direction of exhaust gas flow, the engine and the NO x  reduction assembly in the exhaust gas system. 
     Optionally, the control unit is adapted to receive a signal with a NO x  value indicative of the NO x  content in the exhaust gas from a NO x  sensor being located in a position downstream, as seen in an intended direction of exhaust gas flow, of the NO x  reduction assembly in the exhaust gas system. 
     Optionally, the control unit is adapted to receive a signal indicative of the geographical location of the ship, the control unit further being adapted to determine the NO x  threshold value on the basis of the thus determined geographical location. 
     Optionally, the control unit is adapted to issue a control signal to increase the engine speed of the engine upon detection that the NO x  value exceeds the NO x  threshold value. 
     A sixth aspect of the present invention relates to a control unit for controlling the propulsion of a ship. The ship comprises an engine and a controllable pitch propeller. The engine comprises at least one cylinder. The control unit is adapted to receive a signal indicative of an output set point value. The control unit is also adapted to issue control signals to control the engine speed of the engine and the propeller pitch of the controllable pitch propeller in response to the output set point value. The control signals are determined such that the ship is operated in an operating condition, corresponding to the output set point value, with an engine speed of the engine and a propeller pitch of the controllable pitch propeller such that the fuel consumption of the ship is brought and/or held within a desired fuel consumption range. 
     According to the sixth aspect of the present invention, the control unit is adapted to:
         receive a top pressure signal with a top pressure value indicative of a top pressure in the at least one cylinder and to   issue a control signal to reduce the torque of the engine upon detection that the top pressure value exceeds a top pressure threshold value.       

     Optionally, the control unit is adapted to issue a control signal to increase the engine speed of the engine upon detection that the top pressure value exceeds the top pressure threshold value. 
     Optionally, the control unit is adapted to issue a control signal to reduce the propeller pitch of the controllable pitch propeller in order to reduce the torque of the engine. 
     A seventh aspect of the present invention relates to a ship comprising a control unit according to the fifth or sixth aspect of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples. 
       In the drawings: 
         FIG. 1  illustrates a typical load limit curve for an engine; 
         FIG. 2  illustrates a calculation of an output set value for engine speed and control of torque in order to obtain the correct requested effect; 
         FIG. 3  is diagram of an example control logic, and 
         FIG. 4  is block diagram of an embodiment of a ship. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 4  illustrates an embodiment of a ship  10 . The  FIG. 4  ship comprises an engine  5 , which may also be referred to as a main engine, and a controllable pitch propeller  7 . The torque and engine speed may be adjusted to correspond to an output set point value, e.g. a desired or target engine power output value. Purely by way of example, the output set point value may be set using on-board or remotely located user board  1  illustrated in  FIG. 4 . Generally, the output set point value is indicative of a desired power produced by the engine  5  and the controllable pitch propeller  7 . 
     Purely by way of example, and as indicated in  FIG. 4 , a signal indicative of the output set point value may be sent from the user board  1  to an on-board or remotely located control unit  2 . As a non-limiting example, the control unit  2  may receive information from the engine  5 , an engine speed regulator  4 , a turbo assembly  6 , the controllable pitch propeller  7  and possibly a shaft output sensor  8 . Furthermore, though again purely by way of example, the ship  10  may comprise an additional user board  3  for setup of the system and data reading. 
     Moreover, the control unit  2  may be adapted to issue control signals to the engine  5  and the propeller  7  or a propeller regulating arrangement (not show) to thereby control the engine speed of the engine  5  and the propeller pitch of the controllable pitch propeller  7 . By controlling the propeller pitch, the torque of the engine  5  may be controlled. 
     Additionally, the  FIG. 4  embodiment of the ship  10  comprises a cylinder set comprising least one cylinder  9 . Moreover, in  FIG. 4 , the embodiment of the ship  10  disclosed therein comprises a cylinder pressure sensor  11  adapted to determine the pressure in the at least one cylinder  9 . By way of example, the cylinder pressure sensor  11  may be adapted to determine top pressure in at least one of the cylinders. 
       FIG. 4  also illustrates that the embodiment of the ship  10  illustrated therein comprises an exhaust gas system  12  adapted to guide exhaust gas from the engine  5 . Moreover, as indicated in  FIG. 4 , the exhaust gas system  12  may comprise a NO x  reduction assembly  13 . Purely by way of example, such a NO x  reduction assembly may comprise a catalyst adapted to reduce the NO x  content in the exhaust gases. 
     Further,  FIG. 4  illustrates that the ship  10  may comprise an upstream NO x  sensor  14  located between, as seen in an intended direction of exhaust gas flow, the engine  5  and the NO x  reduction assembly  13 . Instead of, or in addition to the upstream NO x  sensor  14 , the ship may comprise a downstream NO x  sensor  15  located downstream, as seen in an intended direction of exhaust gas flow, of the NO x  reduction assembly  15  in the exhaust gas system  12 . 
     Furthermore, the  FIG. 4  ship  10  comprises a position sensor  16 , which for instance may comprise a global positioning system, adapted to determine the geographical location of the ship  10 . 
     Although the  FIG. 4  embodiment of the ship  10  comprises each one of the cylinder pressure sensor  11 , the upstream NO x  sensor  14 , the downstream NO x  sensor  15  and the position sensor  16 , it is envisaged that other embodiments of the ship  10  may comprise only one of the above sensors  11 ,  14 ,  15 ,  16 . Further, embodiments of the ship  10  are envisaged comprising two or more of the sensors  11 ,  14 ,  15 ,  16 . 
       FIG. 1  illustrates a load limit curve for an engine, for instance the  FIG. 4  engine  5 . As may be gleaned from  FIG. 1 , the graph illustrated therein presents the engine speed (presented as a percentage of maximum engine speed) on the abscissa and the power on the ordinate. Moreover,  FIG. 1  includes isolines for different torque levels (also presented as percentage of the maximum torque producible by the engine). As may be realized from  FIG. 1 , the power produced by the engine increases as the torque increases. In a similar vein, the power produced by the engine increases as the engine speed increases. 
     Moreover, as may be realized from  FIG. 1 , a certain power level may be obtained by a plurality of different combinations of engine torque and engine speed. Generally, from a fuel consumption point of view, it is beneficial to operate the engine at a high torque level. 
     As such, and with reference to  FIG. 2 , upon receipt of an output set point value, for instance indicative of the power produced by the engine, the engine is preferably operated at a condition with a high torque level, for instance at the highest torque level possible in view of the engine&#39;s load limit, and the engine speed is controlled such that the combination of engine speed and engine torque corresponds to the requested power, or the output set point value. 
     However, the present invention proposes also taking additional parameters into account when determining a suitable combination of engine torque and engine speed in order to meet the requested power, or the output set point value. 
     As such, a first aspect of the present invention relates to a method for controlling the propulsion of a ship  10 . The ship  10  comprises an engine  5  and a controllable pitch propeller  7 , wherein torque and engine speed are adjusted to correspond to an output set point value. As has been intimated hereinabove, the torque of the engine may be controlled by controlling the propeller pitch of the controllable pitch propeller  7 . 
     The adjustment of the torque and engine speed is such that the ship  10  is operated in an operating condition with an engine speed of the engine  5  and a propeller pitch of the controllable pitch propeller  7  such that the fuel consumption of the ship is brought and/or held within a desired fuel consumption range. As such, with reference to  FIG. 2 , the engine speed and the propeller pitch are generally controlled such that the engine torque is as high as possible in view of the engine&#39;s load limit curve and also in view of further boundary conditions, as will be elaborated on hereinbelow. 
     According to the first aspect of the present invention, the method comprises:
         determining a NO value indicative of a NO content in the exhaust gas produced by the engine  5  and   reducing the torque of the engine  5  upon detection that the NO x  value exceeds a NO x  threshold value.       

     As such, the above-mentioned NO x  value may be a boundary condition to be used when determining a combination of engine speed and engine torque corresponding to the output set point value and also which results in a fuel consumption within a desired fuel consumption range. 
     The NO x  value may be determined in a plurality of different positions. For instance, with reference to  FIG. 4 , the NO x  value may be determined by evaluating exhaust gas between, as seen in an intended direction of exhaust gas flow, the engine  5  and the NO x  reduction assembly  13  in the exhaust gas system  12 . As such, the NO x  value may be determined using the upstream NO x  sensor  14  in  FIG. 4 . 
     Instead of, or in addition to determining the NO value in the above position, the method may comprise determining the NO value by evaluating exhaust gas downstream, as seen in an intended direction of exhaust gas flow, of the NO x  reduction assembly  13  in the exhaust gas system  12 . As such, the NO x  value may be determined using the downstream NO x  sensor  15  in  FIG. 4 . 
     The NO x  threshold value need not necessarily be constant. Instead, the NO x  threshold value may vary, for instance in dependence on the geographical location of the ship  10 . As such, the method may comprise determining the geographical location of the ship  10 , for instance using a position sensor  16  and determining the NO x  threshold value on the basis of the thus determined geographical location. Purely by way of example, the control unit  2  may comprise a look-up table with different NO x  threshold values for different geographical locations. 
     Moreover, the method may also comprise a feature that the engine speed of the engine  5  is increased upon detection that the NO x  value exceeds the NO x  threshold value. 
     Instead of, or in addition to, using the NO x  value may as a boundary condition when determining a set of engine speed and engine torque that corresponds to the output set point value and which also results in a fuel consumption within a desired fuel consumption range, a top pressure value may be used as a boundary condition. 
     As such, a second aspect of the present invention relates to a method for controlling the propulsion of a ship wherein the method comprises determining a top pressure value indicative of a top pressure in at least one cylinder  9  (see  FIG. 4 ). Purely by way of example, the top pressure value may be determined using a cylinder pressure sensor, such as the cylinder pressure sensor  11  presented hereinabove in relation to  FIG. 4 . Moreover, the method according to the second aspect of the present invention comprises reducing the torque of the engine  5  upon detection that the top pressure value exceeds a top pressure threshold value. 
     Purely by way of example, the top pressure threshold value may be determined in order to reduce the risk of excessive loads and/or excessive wear of the engine  5 . However, instead of, or in addition to, the above, the top pressure threshold value may be determined such that for instance engine emissions are kept within desired ranges. Purely by way of example, a correlation between top pressures and NO x  emissions may be generated and a top pressure corresponding to a maximum desirable NO x  emission level may be used as the top pressure threshold value. 
     In the event that an engine comprises a plurality of cylinders, the top pressure may be measured in one of the cylinders. Alternatively, the top pressure may be measured in two or more of the cylinders and the maximum top pressure measured in the one or more cylinders may be used as the top pressure value which consequently is compared to the top pressure threshold value. 
     Furthermore, as for the method according to the first aspect of the present invention, the engine speed of the engine  5  may be increased upon detection that the top pressure value exceeds the top pressure threshold value. 
     Irrespective of which boundary condition that is used when controlling the propulsion of the ship  10 , the feature of reducing the torque of the engine  5  may comprises reducing the propeller pitch of the controllable pitch propeller  7 . 
     Moreover, it should be noted that each one of the method embodiments presented hereinabove may be carried out by one or more control unit(s), such as the control unit  2  presented hereinabove in relation to  FIG. 4 . As such, the control unit  2  may be adapted to receive signals indicative an output set point value, for instance using the user board  1  illustrated in  FIG. 4 . Moreover, as has been intimated hereinabove, the control unit  2  may also be adapted to receive signals indicative of the engine speed of the engine  5  and the propeller pitch of the controllable pitch propeller  7 . Further, the control unit  2  may also be adapted to receive signals indicative of the relevant boundary condition, e.g. the NO x  value and/or the top pressure value, and to compare the thus received signal to a corresponding threshold value. Moreover, the control unit  2  may be adapted to issue control signals indicative of the engine speed of the engine and the propeller pitch of the controllable pitch propeller in response to the output set point value, taking the above boundary condition into account. 
     As such, the control unit  2  of the ship  10  may be adapted to perform the procedure of any one of the methods presented hereinabove. 
       FIG. 3  illustrates an example of a control logic for a control unit  2 . As may be gleaned from  FIG. 3 , the control logic may comprise a regulator for controlling the engine speed of the engine and the propeller pitch of the controllable pitch propeller. The  FIG. 3  control logic may also comprise means for taking one or more of the above discussed boundary conditions into account when controlling the engine speed and the propeller pitch. As such, the regulator may be adapted to receive sensor signals, such as signals from at least one of the previously discussed cylinder pressure sensor  11 , the upstream NOx sensor  14  and the downstream NOx sensor  15 , and use information in the signals when determining set values for engine speed and torque, i.e. the propeller pitch of the controllable pitch propeller.