Method for controlling the propulsion of a ship

Abstract

The present disclosure 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. The adjustment 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 (10) is brought and/or held within a desired fuel consumption range. The method comprises determining a top pressure value indicative of a top pressure in at least one cylinder (9) and reducing the torque of the engine (5) upon detection that the lop pressure value exceeds a top pressure threshold value.

Claims

1. A method for controlling the propulsion of a ship by a control unit, said ship comprising an engine and a controllable pitch propeller, said engine comprising at least one cylinder, wherein torque and engine speed are adjusted to correspond to an output set point value, wherein the adjustment is such that said ship is operated in an operating condition with an engine speed of said engine and a propeller pitch of said controllable pitch propeller such that the fuel consumption of said ship is brought and/or held within a desired fuel consumption range, the method comprising: determining a top pressure value indicative of a top pressure in said at least one cylinder; and reducing the torque of said engine upon detection that the top pressure value exceeds a top pressure threshold value.

2. The method according to claim 1, wherein the engine speed of said engine is increased upon detection that the top pressure value exceeds said top pressure threshold value.

3. The method according to claim 1, wherein said feature of reducing the torque of said engine comprises reducing the propeller pitch of said controllable pitch propeller.

4. A computer program comprising program code for performing the steps of claim 1 when the computer program is run on a computer.

5. A computer readable medium carrying a computer program comprising program code for performing the steps of claim 1 when the computer program is run on a computer.

6. A control unit for controlling the propulsion of a ship, said ship comprising an engine and a controllable pitch propeller, said engine comprising at least one cylinder, wherein said control unit is adapted to receive a signal indicative of an output set point value, said control unit also being adapted to issue control signals to control the engine speed of said engine and the propeller pitch of said controllable pitch propeller in response to said output set point value, wherein the control signals are determined such that said ship is operated in an operating condition, corresponding to said output set point value, with an engine speed of said engine and a propeller pitch of the controllable pitch propeller such that the fuel consumption of said ship is brought and/or held within a desired fuel consumption range, said control unit further being adapted to: receive a top pressure signal with a top pressure value indicative of a top pressure in said at least one cylinder; and to issue a control signal to reduce the torque of said engine upon detection that said top pressure value exceeds a top pressure threshold value.

7. The control unit according to claim 6, wherein said control unit is adapted to issue a control signal to increase said engine speed of said engine upon detection that said top pressure value exceeds said top pressure threshold value.

8. The control unit according to claim 6, wherein said control unit is adapted to issue a control signal to reduce the propeller pitch of said controllable pitch propeller in order to reduce the torque of said engine.

9. A ship comprising a control unit according to claim 6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

(2) In the drawings:

(3) FIG. 1 illustrates a typical load limit curve for an engine;

(4) 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;

(5) FIG. 3 is diagram of an example control logic, and

(6) FIG. 4 is block diagram of an embodiment of a ship.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(7) 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.

(8) 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.

(9) 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.

(10) 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.

(11) 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.sub.x reduction assembly 13. Purely by way of example, such a NO.sub.x reduction assembly may comprise a catalyst adapted to reduce the NO.sub.x content in the exhaust gases.

(12) Further, FIG. 4 illustrates that the ship 10 may comprise an upstream NO.sub.x sensor 14 located between, as seen in an intended direction of exhaust gas flow, the engine 5 and the NO.sub.x reduction assembly 13. Instead of, or in addition to the upstream NO.sub.x sensor 14, the ship may comprise a downstream NO.sub.x sensor 15 located downstream, as seen in an intended direction of exhaust gas flow, of the NO.sub.x reduction assembly 15 in the exhaust gas system 12.

(13) 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.

(14) Although the FIG. 4 embodiment of the ship 10 comprises each one of the cylinder pressure sensor 11, the upstream NO.sub.x sensor 14, the downstream NO.sub.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.

(15) 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.

(16) 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.

(17) 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'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.

(18) 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.

(19) 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.

(20) 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's load limit curve and also in view of further boundary conditions, as will be elaborated on hereinbelow.

(21) 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.sub.x value exceeds a NO.sub.x threshold value.

(22) As such, the above-mentioned NO.sub.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.

(23) The NO.sub.x value may be determined in a plurality of different positions. For instance, with reference to FIG. 4, the NO.sub.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.sub.x reduction assembly 13 in the exhaust gas system 12. As such, the NO.sub.x value may be determined using the upstream NO.sub.x sensor 14 in FIG. 4.

(24) 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.sub.x reduction assembly 13 in the exhaust gas system 12. As such, the NO.sub.x value may be determined using the downstream NO.sub.x sensor 15 in FIG. 4.

(25) The NO.sub.x threshold value need not necessarily be constant. Instead, the NO.sub.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.sub.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.sub.x threshold values for different geographical locations.

(26) Moreover, the method may also comprise a feature that the engine speed of the engine 5 is increased upon detection that the NO.sub.x value exceeds the NO.sub.x threshold value.

(27) Instead of, or in addition to, using the NO.sub.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.

(28) 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.

(29) 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.sub.x emissions may be generated and a top pressure corresponding to a maximum desirable NO.sub.x emission level may be used as the top pressure threshold value.

(30) 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.

(31) 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.

(32) 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.

(33) 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.sub.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.

(34) 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.

(35) 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.