EP4674747A1

EP4674747A1 - Single propeller vessel motion control based on propeller slip and steering angle

Info

Publication number: EP4674747A1
Application number: EP24186803.3A
Authority: EP
Inventors: Mats RYDSTRÖM
Original assignee: Volvo Penta AB
Current assignee: Volvo Penta AB
Priority date: 2024-07-05
Filing date: 2024-07-05
Publication date: 2026-01-07

Abstract

A computer system (120; 600; 1000) for controlling a propulsion system (105) arranged in a marine vessel (100), the computer system (120; 600; 1000) comprising processing circuitry (122; 1002) configured to: determine a propeller slip (λ) of a single propeller (114) based on an axle speed (ω_P ) of a propeller axle (112), speed data, and a propeller pitch (P); determine a current yaw motion (ω_z ) based on angular velocity data obtained from at least one yaw motion sensor (150); control an axle speed (ω_P ) of the propeller axle (112) based on a relationship between propulsion force generated by the drive unit (110) and the propeller slip (λ) such that the propeller slip (λ) is maintained below a predetermined slip limit (λ_lim ); and control a steering angle (δ_z ) of the drive unit (110) based on a difference between the current yaw motion (ω_z ) and a desired yaw motion (ω_zr ).

Description

TECHNICAL FIELD

The disclosure generally relates to marine propulsion systems. In particular aspects, the disclosure relates to vessel motion control based on propeller slip and steering angle. The disclosure can be applied to marine vessels, such as leisure boats, ships, cruise ships, fishing vessels, yachts, ferries, among other vehicle types. The disclosure is also applicable in unmanned craft such as remote controlled or autonomous sea drones and the like. Although the disclosure may be described with respect to a particular marine vessel, the disclosure is not restricted to any particular marine vessel.

BACKGROUND

Marine propulsion systems cause movement of marine vessels through water, with various designs catering to different operational needs.
Single propeller systems are common due to their simplicity, cost-effectiveness, and ease of maintenance. However, these systems often cause the marine vessel to yaw when accelerating due to the more pronounced propeller walk generated by single propeller systems compared to, e.g., propeller systems comprising dual counter-rotating propellers. These effects can complicate handling of the vessel for example during docking and tight maneuvering, and result in inefficient propulsion, increased fuel consumption, and additional wear on propulsion components, etc. Propeller walk is, however, not necessarily disadvantageous, as more experienced operators can use the propeller walk generated by single propeller systems for delicately maneuvering the vessel, for example in tight docking scenarios.
Duo-propeller solutions, which use counter-rotating propellers, address many of these negative effects by canceling out the torque reaction, improving stability, and increasing overall efficiency. However, duo-propeller systems require more complicated transmissions due to the counter-rotating drive axles that they require.
Improved propulsion systems are desired, in particular when it comes to cost efficiency and vessel maneuverability, as well as passenger comfort.

SUMMARY

According to a first aspect of the disclosure, a computer system is provided. The computer system is for controlling a propulsion system arranged in a marine vessel, the propulsion system comprises a drive unit adapted to drive a single propeller with a propeller pitch via a propeller axle. Aspects of the techniques discussed herein are also applicable to systems comprising more than one drive unit, where each drive unit then comprises a single propeller. The computer system comprises processing circuitry configured to: determine a propeller slip of the single propeller based on an axle speed of the propeller axle, speed data indicative of a speed through water of the marine vessel, and the propeller pitch; determine a current yaw motion of the marine vessel based on angular velocity data indicative of present and/or past angular motion of the vessel, which data is obtained from at least one yaw motion sensor arranged on the marine vessel. The angular velocity data is indicative of a rotational movement of the marine vessel about a vertical axis of the vessel. The computer system is also configured to control an axle speed of the propeller axle based on a relationship between propulsion force generated by the drive unit and the propeller slip such that the propeller slip is maintained below a predetermined slip limit; and control a steering angle of the drive unit based on a difference between the current yaw motion and a desired yaw motion.
The first aspect of the disclosure may seek to solve the problem of maintaining optimal propulsion efficiency and navigational accuracy in a single-propeller marine vessel. A technical benefit may include enhanced stability and maneuverability of the vessel by dynamically adjusting the axle speed and steering angle based on real-time data. The joint steering and slip control provides a more consistent motion of the vessel, especially during acceleration and retardation of the vessel.
Optionally in some examples, including in at least one preferred example, the desired yaw motion is a user-requested propeller walk. A technical advantage may include providing the operator with enhanced control over the vessel's maneuverability by allowing the use of propeller walk. In other words, an operator of the vessel may desire to move the aft section of the vessel sideways, and requests a corresponding propeller walk to cause this desired lateral motion of the vessel stem.
Optionally in some examples, including in at least one preferred example, the processing circuitry is further configured to simultaneously control the axle speed and the steering angle such that the propeller slip is maintained below the predetermined slip limit and the steering angle is controlled based on a difference between the current yaw motion and a desired yaw motion. A technical advantage may include improving overall vessel stability and control by handling both axle speed and steering angle simultaneously. The joint control of propeller slip and steering angle results in less noise due to reduced cavitation, with a controlled amount of propeller walk, together providing an improved vessel behavior in response to a control input from the operator.
Optionally in some examples, including in at least one preferred example, the processing circuitry is further configured to: detect an operational condition of the marine vessel indicating a conflict in said simultaneous control causing the propeller slip to violate the predetermined slip limits and/or failure of the steering angle to be controlled based on said difference between the current yaw motion and the desired yaw motion; and in response to detecting said operational condition, prioritize control of the steering angle over control of the propeller slip. A technical advantage may include ensuring navigational accuracy and vessel safety by prioritizing critical steering adjustments during operational conflicts. By backing off the propeller speed in case the desired yaw motion by the vessel cannot be maintained, undesired steering by the vessel is avoided, which is an advantage.
Optionally in some examples, including in at least one preferred example, the operational condition is a reduction in said speed through water exceeding a brake limit value. A technical advantage may include maintaining vessel stability and control during heavy braking scenarios by adjusting steering priorities.
Optionally in some examples, including in at least one preferred example, the operational condition is an increase in said speed through water exceeding an acceleration limit value. A technical advantage may include ensuring efficient propulsion and control during rapid acceleration by dynamically managing control parameters of the vessel, as will be discussed in more detail below.
Optionally in some examples, including in at least one preferred example, the operational condition is a direction change of the marine vessel exceeding a directional change limit value. A technical advantage may include enhancing maneuverability and safety during sharp turns by effectively managing steering and propulsion.
Optionally in some examples, including in at least one preferred example, the operational condition is an adverse sea condition of an environment where the marine vessel operates. A technical advantage may include improving vessel performance and safety in challenging sea conditions by dynamically adjusting control limits.
Optionally in some examples, including in at least one preferred example, the desired yaw motion is obtained based on one or more of: a predefined navigational course determined by a route planner of the marine vessel, input from a user-operated control interface of the marine vessel, and a collision avoidance algorithm implemented by the computer system. A technical advantage may include providing flexible and adaptive control by incorporating multiple sources of input for determining desired yaw motion.
According to a second aspect of the disclosure, a propulsion system is provided. The propulsion system is arranged in a marine vessel which comprises: a drive unit adapted to drive a single propeller with a propeller pitch via a propeller axle; and the computer system of the first aspect.
The second aspect of the disclosure may seek to solve the problem of integrating an advanced control system with a propulsion drive unit to achieve optimal vessel performance. A technical benefit may include improved coordination between the drive unit and the control system, ensuring efficient propulsion and navigational accuracy.
According to a third aspect of the disclosure, a marine vessel is disclosed. The marine vessel comprises the computer system of the first aspect; and the propulsion system of the second aspect.
The third aspect of the disclosure may seek to solve the problem of implementing an integrated control and propulsion system in a marine vessel for enhanced operational performance. A technical benefit may include seamless integration of propulsion and control systems, resulting in better handling, stability, and efficiency of the marine vessel.
According to a fourth aspect of the disclosure, a computer-implemented method is provided. The method is for controlling a propulsion system arranged in a marine vessel and comprising a drive unit, the drive unit being adapted to drive a single propeller with a propeller pitch via a propeller axle. The method comprises determining, by processing circuitry of a computer system, a propeller slip of the single propeller based on an axle speed of the propeller axle, speed data indicative of a speed through water of the marine vessel, and the propeller pitch; determining, by the processing circuitry, a current yaw motion of the marine vessel based on angular velocity data obtained from at least one yaw motion sensor arranged on the marine vessel, the angular velocity data being indicative of a rotational movement of the marine vessel about a vertical axis; controlling, by the processing circuitry, an axle speed of the propeller axle based on a relationship between propulsion force generated by the drive unit and the propeller slip such that the propeller slip is maintained below a predetermined slip limit; and controlling, by the processing circuitry, a steering angle of the drive unit based on a difference between the current yaw motion and a desired yaw motion.
The fourth aspect of the disclosure may seek to solve the problem of maintaining optimal propulsion efficiency and navigational accuracy in a single-propeller marine vessel. A technical benefit may include enhanced stability and maneuverability of the vessel by dynamically adjusting the axle speed and steering angle based on real-time data.
According to a fifth aspect of the disclosure, a computer program product is provided. The computer program product comprises program code for performing, when executed by processing circuitry, the method of the fourth aspect.
The fifth aspect of the disclosure may seek to solve the problem of providing a software solution for implementing advanced control methods in a marine vessel's propulsion system. A technical benefit may include the ability to deploy and update the control methods easily, enhancing the system's flexibility and adaptability.
According to a sixth aspect of the disclosure, a non-transitory computer-readable storage medium is provided. The non-transitory computer-readable storage medium comprises instructions, which when executed by processing circuitry, cause the processing circuitry to perform the method of the fourth aspect.
The sixth aspect of the disclosure may seek to solve the problem of securely storing and executing control instructions for a marine vessel's propulsion system. A technical benefit may include reliable and efficient execution of control algorithms, ensuring consistent vessel performance and safety.
The disclosed aspects, examples (including any preferred examples), and/or accompanying claims may be suitably combined with each other as would be apparent to anyone of ordinary skill in the art. Additional features and advantages are disclosed in the following description, claims, and drawings, and in part will be readily apparent therefrom to those skilled in the art or recognized by practicing the disclosure as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples are described in more detail below with reference to the appended drawings.

FIG. 1 illustrates an exemplary marine vessel.
FIG. 2 explains the pitch of a propeller, according to an example.
FIG. 3 is a graph showing generated tyre force as function of tyre slip on a road vehicle, according to an example.
FIG. 4 is a graph illustrating example relationships between propeller slip and force.
FIG. 5 is a graph illustrating an example boat speed and propeller slip during launch.
FIG. 6 schematically illustrates example components of a marine propulsion system.
FIG. 7 schematically illustrate aspects of an example computer system.
FIG. 8A illustrates a vessel with two drive units during a yaw motion maneuver, according to an example.
FIG. 8B shows vessel speeds and propeller slips during a yaw motion maneuver, according to an example.
FIG. 9 exemplifies a relationship between motor torque, speed, and efficiency.
FIG. 10 is an exemplary schematic diagram of a computer system according to an example.
FIG. 11 is an exemplary flowchart illustrating a method for controlling a propulsion system according to an example.
FIG. 12 is an exemplary illustration of a computer program product according to an example, and

DETAILED DESCRIPTION

The detailed description set forth below provides information and examples of the disclosed technology with sufficient detail to enable those skilled in the art to practice the disclosure.
The present disclosure addresses the challenge of ensuring that a marine vessel with one or more single-propeller systems can be maneuvered easily and with increased agility. Undesired effects of the propeller walk normally associated with single propeller systems are avoided by a joint control of propeller slip and steering, which ensures that the vessel does not veer in an undesired manner. The joint control of propeller slip and steering ensures that the propeller always has a good grip in the water, without excessive propeller slip that may otherwise cause cavitation that has an undesired effect on both propulsion force and steering capability of the propeller. A computer system is disclosed, featuring processing circuitry configured to determine a propeller slip based on axle speed, speed through water, and propeller pitch. The processing circuitry is further configured to control the axle speed of the propeller axle based on a relationship between propulsion force of the drive unit and the determined propeller slip, maintaining the slip below a predetermined limit to prevent excessive propeller slip which may cause cavitation and noise and a reduction in steering capability of the propeller. Additionally, the processing circuitry is configured to determine a current yaw motion of the marine vessel using angular velocity data indicative of current vessel yaw motion and control a steering angle of the drive unit based on the difference between the current yaw motion and a desired yaw motion to keep the vessel at a desired heading.
Hence, the negative yaw motion reaction is negated similar to a duo-propeller system with counter-rotating propellers, thereby improving maneuverability and stability even in challenging conditions. This control approach enables the vessel to enjoy the efficiency and simplicity of a single-propeller system while achieving performance benefits akin to those of a duo-propeller system.
FIG. 1 schematically illustrates a marine vessel 100, in this case a boat powered by two drive units 110 attached to the transom of the hull 102 of the marine vessel 100. Each drive unit 110 comprises a propeller arrangement 108. The propeller arrangement 108 of the drive units 110 discussed herein is a single propeller arrangement. The present disclosure is not limited to any particular type of marine vessel, nor to any particular type of propeller arrangement. The teachings herein may be used with both outboard drive units and inboard drive units, as well as with both pulling and pushing propellers, provided that it relates to variants of single propeller arrangements. The drive units 110 may be attached to the transom of the marine vessel 100 as illustrated in FIG. 1 or extend down from an underside of the hull 102. The drive units 110 may be rotatable, i.e., provide steering function, or rotationally fixed relative to the hull 102. The drive units 110 and propeller arrangement 108 may form part of a propulsion system 105.
The marine vessel 100 comprises a computer system 120. The computer system 120 is an onboard control system typically integrated into the marine vessel 100, designed to communicate with various computerized units such as sensors, control systems, propulsion systems, Motion Support Devices (MSDs), and the Vessel Motion Management (VMM) module. Processing circuitry 122 within the computer system 120 manages data acquisition and control commands, interfacing with these units either wirelessly or through wired connections using known communication interfaces to ensure seamless operation and coordination of functions the marine vessel 100.
In some examples, propulsion system 105 is an electric propulsion system 105 and the drive unit 110 is an electric drive unit 110. In these examples, each electric drive unit 110 may comprise an electric machine 111 arranged to provide a target axle speed for a propeller axle 112. This may be done upon request from the computer system 120. Electric machines and hybrid electric power sources are becoming more and more common in marine vessels. An advantage with electric machines is that the axle speed of the propeller axle 112 can be controlled rapidly and with higher accuracy. Another advantage is that electric machines allow very quick changes in applied torque.
The forward direction of the marine vessel 100 will be referred to herein as the x-direction, while the lateral direction perpendicular to the forward direction is referred to as the y-direction. The vertical direction is the z-direction, and orthogonal to both x- and y-directions. Velocity in the forward or longitudinal direction of the marine vessel 100 is referred to herein as v_x , while lateral velocity is referred to as v_y. Yaw motion about the z-axis will be referred to as ω_z , as shown in FIG. 1 .
The speed of the marine vessel 100 through the water can be measured by the computer system 120 using a speed log 160. Several different types of marine speed logs are known, such as electromagnetic logs, Doppler logs, impeller-based logs, Pitometer logs, and acoustic co-relation logs.
The speed of the vessel through water may be purely longitudinal, but most likely there is also some drift, i.e., there is a v_y component in addition to the v_x component in the speed. When discussing propeller slip, it is normally the speed of the flow of water passing the propeller in direction of the propeller axle that matters. The speed through water in direction of the propeller axle at a given drive unit will be referred to herein as v_w. This speed v_w is a function of v_x , v_y , and ω_z . It is also a function of the steering angle of the marine drive unit in case the drive unit is a steered (rotatable) drive unit. The steering angle will be discussed in more detail later on in this disclosure. The drive unit can also have an elevation angle, i.e., a thrust direction separated from the horizontal plane by an angle. The present disclosure can be generalized to non-zero elevation angles in a straight-forward manner. The speed v_w can normally be approximated well enough by v_x , and in many cases also by the speed over ground, which can be obtained from, e.g., a satellite positioning system receiver or a sonar system.
The yaw motion ω_z of the marine vessel 100 can be measured by the computer system 120 using a yaw motion sensor 150, such as an inertial measurement unit (IMU) incorporating a gyro, accelerometer, or magnetometer, among others. Various types of inertial measurement units are known, which can provide precise measurements of angular velocity and rotational movement of the vessel. The yaw motion sensor 150 can be arranged anywhere on the marine vessel 100, for example near its center of gravity, provided that it can obtain accurate yaw motion measurements.
The yaw motion sensor 150 detects angular velocity data being indicative of the rotational movement of the marine vessel 100, and the computer system 120 determines the yaw motion ω_z based on said angular velocity data. The rotational movement impacts the overall motion of the marine vessel 100, including any drift, which introduces a lateral velocity component v_y in addition to the longitudinal velocity component v_x. In this disclosure the term "current" is used in contexts of the yaw motion. This emphasizes the yaw motion being determined currently, i.e., during operation, for example in (at least near) real-time, ensuring that the system's adjustments and responses are based on the most up-to-date and accurate information about the vessel's rotational movement. This capability is important for maintaining control and stability of the marine vessel under dynamic conditions. It is understood that the term "current" as used herein does not refer to sea currents, i.e., movement of water, nor electrical currents.
FIG. 2 schematically illustrates a single propeller 200 having a propeller diameter D and a pitch P. The pitch P is the distance travelled by the propeller as it is being screwed into an imagined solid medium. The rotation velocity of the propeller is denoted ω_P.
Longitudinal wheel slip λ_x for a tyre on a road vehicle such as a truck or car can be defined as $λ_{x} = \frac{{Rω}_{x} - v_{x}}{\max (|{Rω}_{x}|, |v_{x}|)}$ where R is an effective wheel radius in meters, ω_x is the angular velocity of the wheel (where the subscript x is for indicating that the wheel normally travels in the longitudinal direction), and v_x is the longitudinal speed of the wheel in the coordinate system of the wheel (relative to the road). Wheel slip is, in essence, a speed difference measured between the wheel and the vehicle. If the wheel accelerates in rotational motion faster than the road vehicle accelerates over the road surface, then the wheel slip increases. Wheel slip during acceleration is positive while wheel slip during braking is negative. In order for a wheel or tyre on a road vehicle to produce a tyre force, slip must occur. This is true for both acceleration and for braking. For smaller slip values the relationship between wheel slip and generated force is approximately linear due to the fact that there is full adhesion in the tyre contact patch and no sliding occurs, where the proportionality constant is often denoted as the slip stiffness of the tyre. The normal force F_z acting on the tyre of a wheel is key to determining some important vehicle properties. For instance, the normal force to a large extent determines the achievable longitudinal tyre force F_x by the wheel since, normally, F_x ≤ µ F_z , where µ is a friction coefficient associated with a current road friction condition.
An inverse tyre model is a model of wheel behavior which describes tyre force generated in longitudinal direction in the rolling direction as function of wheel slip. FIG. 3 is a graph 300 showing an example of tyre force as function of longitudinal wheel slip λ. The longitudinal tyre force F_x shows an almost linearly increasing part 310 for small wheel slips, followed by a part 320 with more non-linear behavior for larger wheel slips. At this stage part of the contact patch is sliding relative to the road surface. It is noted that there is a peak 330, beyond which the tyre force declines with wheel slip, i.e., if the wheel speed is increased beyond a given wheel speed, the generated tyre force will decline. The main reason for the declining characteristics is that sliding friction is lower than the friction. Control of a road vehicle in the region 320 may be difficult and is therefore often avoided, and it is also undesired from an energy efficiency point of view as well as from a tyre wear perspective. Operation in the region 320 is often also associated with a reduced comfort level for the passengers in the road vehicle. Therefore, a wheel slip limit is λ_lim is often imposed in order to ensure that the wheel does not operate in the undesired region 320, at least not for prolonged periods of time.
The longitudinal slip λ_x of a propeller can be defined in a manner analogous to that of a tyre on a road vehicle as the difference between the pitch P of the propeller divided by the time for one revolution and the speed of the propeller through the water (STW) in direction of the propeller axle, i.e., v_x if the boat is travelling straight ahead, and a combination v_W of v_x , v_y, ω_z if the boat is maneuvering. The propeller speed through water (v_P ) without slip is the speed of the propeller if the propeller is seen as a screw being screwed into a solid medium, i.e., the pitch distance P divided by the time for one complete revolution of the propeller (2π/ω_P ), according to the formulas below: $λ_{x} = \frac{v_{W} - v_{P}}{\max (|v_{P}|, |v_{W}|)}$ $v_{P} = \frac{{Pω}_{P}}{2 π}$
If the propeller is accelerated the slip increases and vice versa. Propeller slip can be both positive (during acceleration) and negative (during retardation). Other alternative propeller slip definitions may be used with the same or similar effect, such as discretized approximations of the above expression.
It has been realized that a similar relationship as that in FIG. 3 exists between propeller thrust and propeller slip for many propeller and hull shape combinations. As the propeller is accelerated the propeller slip increases and it starts to generate thrust. At first thrust increases with propeller slip, such that the higher the propeller slip the higher the thrust. Again, analogous to the situation with road vehicle tyres - without propeller slip there cannot be any thrust acting on the hull of a marine vessel. However, once the propeller slip has increased beyond a critical point, cavitation starts to develop, and a situation akin to the non-linear region 320 is seen where more propeller speed results in reduced thrust (or at least reduced thrust coefficient) and/or increased discomfort due to generation of noise and vibration. Propeller wear caused by the cavitation also sets in as propeller slip goes beyond a given propeller slip value.
Because of propeller rotation through the water at an angle of attack, a pressure side and a suction side are created on each of the propeller's blades. The faster the blades cut through the water, i.e., the faster it rotates relative to the STW, the lower the pressure on the suction side of the blades becomes. At a certain propeller speed relative to STW, the pressure on the suction side becomes so low that the water flowing over that area evaporates, forming vapor bubbles or voids. When this happens, the efficiency of the propeller operation starts to decline.
The effects of cavitation on propulsion performance can be considerable. Cavitation usually starts at the blade tips and spread gradually over the entire blades as the propeller loading is increased. When cavitation has extended to about 0.75 of the radius it is found there is a considerable loss in thrust followed by a reduction in torque which means in practice that, there will be a marked increase in revolutions for a given power. Since the thrust breakdown proceeds more rapidly than the change in torque there can be a considerable loss in efficiency. Noise and vibration are other undesired effects which result if cavitation becomes too pronounced.
FIG. 4 illustrates some example relationships between thrust, i.e., propulsion force, and propeller slip that can be seen for some propeller design and hull shape combinations. There is an approximate linear region 410 where increasing propeller speed results in increase propeller thrust. If the propeller speed relative to the speed of the vessel through water is increased beyond this range, a peak range 420 is entered where the propeller operates at peak efficiency. Beyond this range a region 430 is seen where increased propeller speed is detrimental to both propulsion force and energy efficiency.
In the first example 440, propulsion force increases with propeller slip up to a point where no more thrust is obtained, regardless of how much the propeller speed is increased. In this case is does not make sense to increase propeller speed beyond a certain point, since the additional increase only gives rise to inefficiency and often also discomfort manifested as noise and vibration. Propeller wear may also increase in the region 430.
In the second example 450 the propeller design and the hull shape together are such as to result in an approximately linear increase in propulsion force with increasing propeller speed up to a point where cavitation starts to be so pronounced as to act detrimental to the thrust. The thrust then starts to decrease if the propeller is rotated faster relative to the surrounding water.
In the third example 460 the effects of cavitation are more dramatic. In this case the propeller design and hull shape combination are such as to result in a catastrophic cavitation which results in a near total loss of propulsion force.
In all examples 440, 450, 460 the generated noise and vibration is at first relatively small, and then increases sharply as the propeller slip reaches high enough values.
Notably, each scenario has a propeller slip limit λ _x1, λ _x2, λ _x3 below which efficient and predictable operation is to be expected, and beyond which a more unpredictable and less efficient operation is more likely, where noise and vibration are also more pronounced. Hence, for each combination of propeller design and hull shape, there is a desired propeller slip range of operation, beyond which inefficient and/or uncomfortable operation ensues.
As mentioned, the relationship between thrust and propeller slip depends on many factors such as propeller design, hull shape, temperature, air pressure and sea conditions. However, an approximate relationship between propeller thrust and propeller slip can often be established from computer simulation, mathematical analysis, and/or practical experimentation in a straight-forward manner. Different amounts of propeller slip can be generated, and the thrust can be measured for each propeller slip value. The measured and/or simulated thrust levels can then be plotted against the propeller slip values to obtain a relationship like those in FIG. 4.
Some marine drive units are better controlled based on propeller slip or, equivalently, based on propeller speed relative to the STW, compared to control based propeller axle torque as is the more or less prevailing control method today. At the very least, advantages may be obtained if a propeller slip limit is implemented, where the marine drive unit is prevented from operating at a propeller slip beyond a predetermined slip limit. Since operation beyond the slip limit rarely brings any benefits when it comes to boat handling, propulsion efficiency, or drive component wear. The present disclosure therefore presents a computer system 600 (cf. computer system 120 of FIG. 1 ) and corresponding methods for controlling a drive unit 110 on a marine vessel 100, such as a leisure craft or a smaller commercial vessel, i.e., a ferry, small freight boat, or the like. The computer system 600 is configured to obtain data indicative of a speed through water (STW) v_W of the vessel 100. The STW may be obtained using a traditional speed log and/or via other means, such as a global positioning system receiver, as mentioned above. The relevant speed through water here is the speed through water measured along the extension direction of the propeller axis, i.e., the speed of the water that the propeller sees. The data indicative of a speed through water may also be related to the speed through water in front of the propeller, often referred to as v_A. This speed is often lower than the STW, since the hull pulls an amount of water with it as it travels through the water. The two are at least approximately related as v_A = v_W (1 - w), where w is the boat wake number. Different hulls have different wake numbers.
The STW of the marine vessel 100 is normally a combination of longitudinal, lateral and yaw motion, although it can often be approximated well enough by the longitudinal speed of the hull through the water, i.e., v_x. The computer system 600, depending on the available sensor data, may be configured to determine this speed through water using a single log, or a collection of different sensors. The computer system 600 is configured to determine a propeller slip λ of the drive unit 110 based on a propeller speed ω_P of the drive unit 110 and on the speed through water v_W of the marine vessel 100. This propeller slip is indicative of how fast the propeller spins in relation to the speed of the water passing the propeller, the faster the propeller spins relative to the speed of the water passing the propeller the higher the slip is. If the marine vessel 100 is almost stationary, then a relatively small propeller speed may give rise to large slip, while a marine vessel 100 moving fast through the water requires a substantial propeller speed to generate the same propeller slip. Very large propeller slips can often be seen during launch of the vessel if the drive unit is powered by an electric machine, since the applied torque by an electric machine is almost instantaneous in response to a control command from the helm and does not build up over a transient time period as is normally the case with combustion engines. The computer system 600 is arranged to control the propeller speed ω_P of the drive unit 110 to maintain the propeller slip λ below a predetermined propeller slip limit λ_lim , to ensure that the propeller operates in the desired region 410 or in the peak thrust region 420, and not in the undesired region 430 discussed in connection to FIG. 4 .
FIG. 5 shows a graph 500 that illustrates an example marine vessel launch operation in terms of propeller axle speed ω_P and vessel speed v_W through water as function of time. A constant acceleration is assumed for this simplified illustrative example. The vessel speed through water v_W is shown by the solid line 510, and the propeller speed ω_P is shown by the dashed line 520. At time T ₀ the boat starts to accelerate from standstill in the water. The propeller speed is therefore increased to a point ω ₀ corresponding to a propeller slip λ which results in close to optimal thrust, i.e., a propeller slip somewhere in or around the region 420. The maximum propeller speed ω_max is illustrated by the dash-dotted line 530, and it is noted that the propeller is not accelerated immediately up to this maximum speed, since this would mean that the propeller-hull combination ends up in the undesired high-slip region 430 discussed above in connection to FIG. 4 . Instead, the propeller speed is increased gradually as the vessel picks up speed though the water, always ensuring that the speed difference between the propeller speed and the vessel speed through water, i.e., the propeller slip λ is kept close to the propeller slip that corresponds to the peak region 420 in FIG. 4 .
Aspects of the techniques discussed herein can also be used to achieve a desired level of propeller thrust in an efficient manner by controlling the propeller slip to be at a value corresponding to the desired level of propeller thrust. In particular, there is disclosed herein a computer system 600 for controlling a propeller-based drive unit 110 on a marine vessel 100. The computer system 600 can be used separately from that configured to limit propeller speed to speeds below the propeller slip limit, and the two can also be combined with advantage. The computer system 600 is configured to obtain data indicative of a speed through water v_W of the marine vessel 100, and also configured to obtain a relationship 400 between drive unit thrust F_x and propeller slip λ. The computer system 600 is furthermore configured to obtain data indicative of a desired thrust to be generated by the drive unit 110, and to determine a target propeller slip corresponding to the desired thrust, based on the relationship 400 between drive unit thrust F_x and propeller slip λ. The computer system 600 is then able to control propeller speed ω_P of the drive unit 110 to generate the target propeller slip which provides the desired thrust.
The relationship 400 between drive unit thrust F_x and propeller slip λ may be configured as a predetermined analytical function or a collection of predetermined analytical functions. These functions can be determined based on computer simulation or by practical experimentation, or by a combination of computer simulation and practical experimentation. Mathematical analysis can also be used in the derivation of these relationships. The relationships do not need to be very exact, approximate relationships, such as linear approximations, have been found to give good results in many cases. The relationship 400 between drive unit thrust F_x and propeller slip λ can also be realized as a preconfigured look-up table (LUT), allowing translation from thrust to propeller slip and back by indexing into the LUT.
FIG. 6 shows some example components of a computer system 600 for controlling a propeller-based drive unit 110 on a marine vessel 100. A vessel operator provides control commands 615 to the system 600 from the marine vessel helm 610. The control commands may comprise a desired acceleration a_req and a desired curvature c_req that the vessel motion is to follow. The vessel operator is often a person using a steering input device and a throttle control, but it can also be a computerized controller that operates the boat on autopilot. So-called driver assistance systems are also known where the boat is controlled by a blend of human operator input and computer control.
The control commands 615 are received by a vessel motion management (VMM) module 620 that translates the high level commands into lower level actuator controls 625 sent to one or more motion support device (MSD) control modules 630. The MSD control modules 630 then control physical actuators on the marine vessel 100, such as propulsion 640, transmission 650 and steering 660, by issuing suitable control commands 645, 655, 665. The speed through water v_W is obtained from one or more STW sensors 670. These sensors often but not necessarily comprise a speed log arranged on the marine vessel 100 but may also comprise satellite positioning system receivers and sonar systems arranged to measure speed over ground, which is indicative of the STW, even though they are approximations. Thus, both the MSD control modules 630 and the VMM module 620 may obtain information indicative of the speed of the boat through water. The system components are also able to determine the propeller speed ω_P , since the transmission setting T is known to the system 600 and also the output axle speed ω_A of the propulsion device 640. In case the propulsion device 640 comprises an electric machine, then the motor axle speed of the electric machine is inherently known from the motor drive circuit. The teachings herein are particularly suitable for use with electric machines that can be controlled to deliver a target axle speed in an accurate manner. In case the propulsion device is some other type of engine, such as a combustion engine, then the axle speed can be determined by an axle speed sensor or the like.
With reference also to FIG. 7 , the VMM module 620 continuously transforms the acceleration profiles a_req and curvature profiles c_req received from the helm 610 into control commands 631, 632 for controlling vessel motion functions, actuated by the different MSD control modules 630 of the marine vessel 100, i.e., the different propulsion resources and steering resources on the marine vessel 100. Other systems on the marine vessel 100 may also be controlled by the VMM function, such as ballast tanks, interceptors, gyros, and the like.
The VMM module 620 performs vessel state or motion estimation 720, i.e., the VMM module 620 continuously determines a current vessel state at time t, s(t), comprising, e.g., position, speed, acceleration, and yaw motion by monitoring operations using various sensors 710 arranged on the marine vessel 100, such as the speed logs mentioned above, satellite positioning system receivers, and yaw motion sensors, e.g. IMUs. The VMM module 620 optionally also performs motion prediction 730, i.e., estimates a future vehicle state s (t + T) at one or more time instants t + T in the future. Both motion estimation 720 and motion prediction 730 are generally known techniques, and several example implementations exist in the literature. These sub-functions will therefore not be discussed in more detail herein.
The result of the motion estimation 720 and the optional motion prediction 730, i.e., the estimated vehicle state s (t), and possibly also the predicted future vehicle state set s (t + T), is input to a force generation module 740 which determines the required global forces to cause the marine vessel 100 to move according to the requested acceleration and curvature profiles a_req , c_req. This actuation may comprise both propulsion and steering, i.e., actuation of both propulsion units and rudders.
The required global force vector is in this example input to an MSD coordination module 750 which allocates forces and coordinates actuators. The coordinated actuators then together provide the desired lateral F_y and longitudinal F_x forces on the marine vessel 100, as well as the required moments M _z, to obtain the desired motion by the marine vessel 100. The MSD coordination module 750 optimizes MSD allocation with a primary obj ective to meet the required global forces. The MSD coordination module 750 outputs one or more target propeller slip values {λ_i }_i=1..N and one or more rudder angles {δ_i }_i=1.. _N. Suppose for instance that an acceleration of the marine vessel 100 is requested from the helm, then an increase in propeller slip is called for in order to generate an increased propeller thrust. However, the increase in propeller slip will not be so large as to result in inefficiency, i.e., the propeller slip will not pass beyond the propeller slip limit imposed by the system. In case a curvature is requested, then some steering may be applied, possibly in combination with a difference in propeller slips in case two or more drive units are installed on the vessel.
One or more interfaces 631, 632 pass from the VMM module 620 to the different MSD control modules 630 on the boat, such as electric machine controllers, combustion engine controllers, and rudder controllers.
The VMM module 620 may be arranged to request a propeller slip λ from the MSD control module(s) 630, and/or a propeller speed ω_P from the MSD control module(s) 630.
FIG. 8A illustrates an example marine vessel 100 that is executing a turning maneuver 800. This marine vessel 100 has two drive units, one on the starboard side and one on the port side. There are also two speed logs STW-L and STW-R configured to measure a speed through water for each of the drive units. With the propeller slip-based control methods discussed herein, it is noted that the propeller speed of the port-side propeller will be slightly lower compared to the starboard side propeller, since the starboard side propeller is travelling faster through the water due to the curvature. The two propellers are still operated at the same slip value λ = A, i.e., at the desired target propeller slip. This is illustrated in FIG. 8B , which shows a graph of propeller speed, where the upper solid curve 860 is the propeller speed of the starboard side drive unit and the lower dashed curve 870 is the propeller speed of the port side drive unit. Since the two propellers are operating at the same speed, the thrust is about the same on both drive units. However, the VMM function may of course choose to allocate more or less propeller speed, i.e., a difference in propeller slip, in case a difference in thrust is wanted, e.g., to aid in steering.
Looking at the example in FIG. 8A , it is understood that is may be advantageous to use separate speed logs when there are more than one drive unit 110 on the marine vessel 100. According to some aspects, the computer system 600 is arranged to control a plurality of drive units 110 on the marine vessel 100. The computer system 600, 1000 is configured to obtain the data indicative of speed through water v_W separately for at least two drive units 110 out of the plurality of drive units 110.
According to some aspects, the computer system 600 is arranged to configure a lower propeller slip limit $λ_{\lim}^{o}$ for the outer drive unit 820 compared to the propeller slip limit $λ_{\lim}^{i}$ for the inner drive unit 810 in a dual drive unit system performing a turning maneuver. The difference between the two slip limits can, e.g., be configured as function of the curvature of the turning maneuver, or the roll angle of the vessel during the turning maneuver. This way the outer drive unit which is probably operating at reduced draught will not exhibit the same amount of cavitation due to the reduced draught.
FIG. 9 is an efficiency map 900 of an example electric machine 111. The motor speed of the electric machine 111 is plotted on the x-axis and the applied torque by the electric machine 111 is plotted on the y-axis. The contour plot then shows efficiency of the electric machine 111, i.e., how much of the input power that is converted into motion and how much that is lost as heat etc. The shape of this map is similar for most electric machines. This example electric machine 111 is able to provide a high torque for low axle speeds, and the maximum achievable applied torque then declines with axle speed. It is noted that, for each propeller speed there is a best applied torque. Hence, for a given speed 910, it is possible to find an applied torque 920 that maximizes the efficiency of the electric machine operation. Conversely, for a given applied (positive) torque, there is an axle speed that maximizes efficiency.
According to some aspects, the computer system 600 is arranged to control a drive unit 110 having an adjustable propeller pitch P. The computer system 600 is arranged to control the propeller speed ω_P and the propeller pitch P of the drive unit 110 to generate a target propeller slip λ, based on a predetermined relationship 900 between efficiency, axle speed, and applied torque of an electric machine. According to an example, the propeller slip λ is first determined based on the motion requests received from the helm 610 of the marine vessel 100. This target propeller slip can be translated into an equivalent motor axle speed using information about the transmission setting and the STW v_W of the marine vessel 100. Given this motor axle speed, the efficiency map can be consulted, and the desired, typically optimal, pitch can be found by a straightforward linear search. The electric machine 111 will then generate the target propeller slip at an efficiency that is as high as possible given the request from the helm.
Propeller walk, also known as propeller effect, wheeling effect, paddle wheel effect, asymmetric thrust, asymmetric blade effect, transverse thrust, or prop walk, is the tendency of a propeller to induce a rotational movement about the vertical axis (also known as the yaw motion ω_z as discussed herein) in addition to forward or backward acceleration. For instance, a right-handed propeller in forward gear will push the stern to starboard, causing the bow to turn to port and the boat to turn counter-clockwise, while in reverse gear, the effect is stronger and in the opposite direction. Conversely, a left-handed propeller induces the opposite rotational effects.
It has been recognized that the tendency of a propeller to induce rotational movement about the vertical axis of the vessel 100 can be beneficially utilized for maneuvering in certain situations. The present disclosure therefore distinguishes desired propeller walk from undesired propeller walk. Propeller walk is considered undesired when it causes unintended rotational movements that negatively impact navigation, such as during straight-line acceleration or acceleration along a path having a desired curvature. The present control scheme compensates for undesired propeller walk to maintain stable navigation, while allowing controlled propeller walk when requested by the operator for improved maneuverability, such as during docking.
The present control scheme controls propeller slip and steering jointly, i.e., concurrently. This means that the single propeller will have a better grip in the water due to the absence of excessive propeller slip during steering. This improved grip enhances the propeller's capability to steer the vessel. The joint control of propeller slip and steering addresses a single, integrated problem as it ensures that both propulsion and directional control are improved simultaneously. For example, during acceleration, the system can adjust the propeller's axle speed to maintain desired slip while simultaneously modifying the steering angle to align with the desired yaw motion. This joint approach can prevent excessive slip, which can lead to inefficiency and instability, and ensures that the vessel follows its intended path. Similarly, during deceleration, the system reduces propeller slip to maintain control and stability, while adjusting the steering angle to counteract any rotational forces induced by the deceleration process.
By improving both propulsion and steering concurrently, the vessel can perform precise maneuvers, such as tight turns or docking, with greater ease and accuracy. This can be particularly advantageous in congested or confined waterways where precise control is essential. Moreover, the reduction in propeller slip during maneuvering can lead to increased passenger comfort. Excessive propeller slip can cause cavitation, which generates unwanted noise and vibration. By minimizing slip, the system reduces cavitation, resulting in a smoother and quieter ride for passengers. Additionally, the joint control scheme can enhance fuel efficiency. By preventing excessive slip, the system can ensure that the propeller operates within its optimal efficiency range, reducing fuel consumption. This not only lowers operational costs but also contributes to environmental sustainability by reducing the vessel's carbon footprint.
In summary, the joint control of propeller slip and steering can provide a comprehensive solution to an integrated problem of maintaining optimal propulsion and directional control. It can enhance vessel maneuverability, improve passenger comfort, and increase fuel efficiency, making it a highly effective approach for modern marine vessel control systems.
By obtaining angular velocity data during operation of the marine vessel 100, the current propeller walk can be determined. The computer system 100 can then automatically compensate for any undesired propeller walk in a nominal driving state of the marine vessel 100. The nominal driving state refers to the condition where the marine vessel 100 operates under standard, expected conditions without any significant disturbances or deviations, maintaining steady and controlled navigation. This compensation enables the marine vessel 100 to drive straight forward, for example while accelerating, without the negative turning effects caused by undesired propeller walk. This compensation also enables the marine vessel 100 to accelerate along a path having a curvature without deviating from the curved path due to the turning effects caused by undesired propeller walk. The present inventor has realized that this can be achieved through a sophisticated combination of control of the axle speed ω_P of the propeller axle 112, as extensively discussed herein, and control of a steering angle δ_z , thereby ensuring precise and stable navigation, as well as ensuring that the propeller has a good grip in the water. This control approach enables the marine vessel 100 to enjoy the efficiency and simplicity of a single-propeller system while achieving performance benefits akin to those of a duo-propeller system.
The control of the steering angle δ_z is based on a difference between the current yaw motion ω_z and the desired yaw motion ω_zr , i.e., the steering angle δ_z is adapted to reduce the difference between current yaw motion ω_z and desired yaw motion ω_zr . If the vessel veers to starboard then counter-steering to port is applied, and vice versa. As discussed in connection to FIG. 1 , the current yaw motion ω_z of the vessel 100 is determined based on angular velocity data obtained from at least one yaw motion sensor 150. The steering angle δ_z is the angle at which the drive unit 110 or rudder of the marine vessel 100 is positioned relative to the longitudinal axis of the marine vessel 100 to control its direction of travel. The steering angle δ_z determines the direction and degree of the turn of the marine vessel 100, enabling the marine vessel 100 to navigate along a desired path, which path may be straight or have some curvature.
In some examples, a predefined navigational course determined by a route planner can set the desired yaw motion ω_zr . The route planner of the marine vessel 100 generates a predefined navigational course based on the starting point, destination, and any waypoints along the route. This course takes into consideration various factors such as optimal travel time, fuel efficiency, and safe navigation through known waterways. The desired yaw motion ω_zr is in these examples derived from this predefined course, ensuring that the marine vessel 100 follows the planned route accurately, while automatically compensating for any undesired propeller walk.
In some examples, a user-operated control interface can retrieve the desired yaw motion ω_zr which may be set by the computer system accordingly. The marine vessel 100 is equipped with a user-operated control interface that allows the operator to manually input steering commands. These commands can be used to adjust the desired yaw motion ω_zr in real-time based on the operator's intentions. For example, if the operator wants to make a sharp turn or navigate through a narrow channel, the input from the control interface will directly influence the desired yaw motion ω_zr , with the system automatically compensating for undesired propeller walk to execute the maneuver smoothly.
In some examples, a collision avoidance algorithm implemented by the computer system can be configured to set the desired yaw motion ω_zr. The computer system implements a collision avoidance algorithm that continuously monitors the surrounding environments of the marine vessel 100, for instance utilizing various sensor data. This algorithm identifies potential obstacles and calculates the safest path to avoid collisions. The desired yaw motion ω_zr is adjusted based on the output of the collision avoidance algorithm, ensuring that the marine vessel 100 navigates safely around obstacles while maintaining a stable course. The system dynamically compensates for undesired propeller walk during these adjustments to prevent unintended rotational movements of the vessel 100.
In some examples, the centralized VMM module 620 as discussed herein can be configured to request the desired yaw motion ω_zr from at least one MSD control module 630. The VMM module 620 translates high-level control commands from the helm 610 into lower-level actuator controls, which are then sent to the MSD control module(s) 630. These MSD control modules 630 manage physical actuators on the marine vessel, such as propulsion 640, transmission 650, and steering 660, by issuing appropriate control commands. The VMM module 620 continuously monitors the state of the marine vessel 100 using sensors, including speed logs, satellite positioning systems, and IMUs, to determine parameters such as speed, acceleration, and yaw motion.
For instance, if a navigation command is received from the helm 610, the VMM module 620 will request a desired yaw motion ω_zr to align with a predefined navigational course. Similarly, input from a user-operated control interface can adjust the desired yaw motion ω_zr in real-time according to the operator's steering commands. Additionally, a collision avoidance algorithm implemented by the computer system can dynamically adjust the desired yaw motion ω_zr to navigate safely around obstacles, ensuring the vessel maintains a stable course. By leveraging the capabilities of the VMM module 620 to request and manage the desired yaw motion ω_zr , the system may ensure precise and responsive control of the orientation of the marine vessel 100, enhancing navigational accuracy and safety.
By integrating these sources of input mentioned above, and others, the computer system can ensure that the desired yaw motion ω_zr is aligned with the desired, typically optimal, navigational strategy, whether it is following a predefined route, responding to manual steering commands, avoiding obstacles, or complying with one or more requests to one or more MSD control modules 630. This comprehensive approach can provide enhanced control and safety while leveraging the benefits of a single-propeller system.
As previously discussed, propeller walk is typically an undesirable steering effect, particularly during maneuvering of the marine vessel 100 in its nominal state. However, in specific instances the operator may prefer to utilize propeller walk to enhance maneuverability. In such cases, the operator can request the desired yaw motion ω_zr that leverages the propeller walk effect. This allows the steering angle δ_z to be controlled in accordance with the desired propeller walk, enabling the operator to partially compensate for the current yaw motion ω_z rather than fully counteracting it. This partial compensation results in a controlled amount of propeller walk, which can be advantageous in certain scenarios, such as docking. Steering and propeller walk can also be used jointly by the VMM module 620 of the vessel 100 to bring about a more pronounced lateral stem motion of the vessel 100. Experienced operators may find that the inherent drift and turning characteristics induced by propeller walk provide greater freedom and precision when positioning the marine vessel 100 at a docking location. By modulating the automatic compensation of propeller walk, the system allows the operator to achieve the desired maneuvering effect, thereby improving handling and control of the marine vessel 100 during complex maneuvers. In essence, the ability to adjust the degree of propeller walk compensation can provide a versatile tool for operators, enhancing the adaptability and responsiveness of the marine vessel 100 in various operating conditions.
In some examples, simultaneous control of both the axle speed ω_P and the steering angle δ_z can be enabled. This may be achieved through the VMM module 620 and one or more MSD control modules 630. The term "simultaneous" in these contexts refers to the ability of to manage both axle speed ω_P and steering angle δ_z concurrently. For example, during acceleration while turning, the VMM module 620 can adjust the axle speed for thrust and the steering angle for the desired turn without exceeding operational limits. In another example where rough seas are prevailing, the VMM module 620 can reduce axle speed and adjust the steering angle to counteract lateral forces, maintaining the vessel's course. In yet another example during collision avoidance, the VMM module 620 can balance speed reduction and sharp turns to navigate around obstacles safely.
Where said simultaneous control is carried out, one or more operational condition that may indicate a conflict in the simultaneous control can be detected. The operational condition can be manifold, and is typically detected in response to the propeller slip λ exceeding propeller slip limit λ_lim , and/or a failure to control the steering angle δ_z accurately based on the difference between the current yaw motion ω_z and the desired yaw motion ω_zr . Hence, an inefficiency or potential damage is identified, ultimately leading to a navigational inaccuracy.
In order to detect the operational condition, certain control algorithms can be employed to continuously compare the monitored parameters against predefined thresholds and limits. The operational condition may be a reduction in speed through water v_W exceeding a brake limit value, typically occurring during heavy braking, similar to the Automatic Braking System (ABS) in cars. The operational condition may be an increase in speed through water v_W exceeding an acceleration limit value, typically occurring during heavy acceleration. The operational condition may be a direction change of the marine vessel 100 exceeding a directional change limit value, typically occurring during heavy turning. The operational condition may be an adverse sea condition of the environment where the marine vessel 100 operates. Adverse conditions, such as heavy waves or strong sea currents, can exceed a certain limit set by the system. These limits can be determined based on environmental data, historical performance, or the like. The operational condition may be an automatic collision avoidance maneuver of an automatic control functionality of the marine vessel 100. This condition can arise during auto-docking or dynamic obstacle avoidance modes, which may involve speed adjustments and/or turning maneuvers.
A learning system can be configured to automatically update the various limits based on real-time data and historical performance. For instance, if the marine vessel 100 frequently encounters specific sea conditions, the learning system can adjust the limit for adverse sea conditions accordingly. Similarly, the learning system can refine acceleration, braking and/or directional change limit(s) based on observed responses to different maneuvers. By doing so, the learning system can ensure that the threshold limits remain optimal and adaptive to changing conditions.
Upon detecting an operational condition, for example using any of the methods discussed above, control of the steering angle δ_z is prioritized over control of the axle speed ω_P. Due to safety reasons, it may be important to ensure that the marine vessel 100 maintains its intended course and navigational accuracy, even if it means temporarily allowing the propeller slip to exceed its optimal range. When a conflict is detected, the VMM module 620 may dynamically adjust its control strategy to prioritize steering angle adjustments. This involves recalculating the required global forces and reallocating them to the propulsion and steering systems to achieve the desired yaw motion ω_zr . For instance, if the marine vessel 100 encounters rough sea conditions that cause the propeller slip to exceed the limit, the prioritization scheme will cause focus on maintaining the correct steering angle to navigate safely through the conditions. The priority of controlling the axle speed ω_P is accordingly reduced until the steering angle δ_z is stabilized and the marine vessel 100 is back on its desired course.
FIG. 10 is a schematic diagram of a computer system 1000 for implementing examples disclosed herein. The computer system 1000 is adapted to execute instructions from a computer-readable medium to perform these and/or any of the functions or processing described herein. The computer system 1000 may be connected (e.g., networked) to other machines in a LAN (Local Area Network), LIN (Local Interconnect Network), automotive network communication protocol (e.g., FlexRay), an intranet, an extranet, or the Internet. While only a single device is illustrated, the computer system 1000 may include any collection of devices that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. Accordingly, any reference in the disclosure and/or claims to a computer system, computing system, computer device, computing device, control system, control unit, electronic control unit (ECU), processor device, processing circuitry, etc., includes reference to one or more such devices to individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. For example, control system may include a single control unit or a plurality of control units connected or otherwise communicatively coupled to each other, such that any performed function may be distributed between the control units as desired. Further, such devices may communicate with each other or other devices by various system architectures, such as directly or via a Controller Area Network (CAN) bus, etc.
The computer system 1000 may comprise at least one computing device or electronic device capable of including firmware, hardware, and/or executing software instructions to implement the functionality described herein. The computer system 1000 may include processing circuitry 1002 (e.g., processing circuitry including one or more processor devices or control units), a memory 1004, and a system bus 1006. The computer system 1000 may include at least one computing device having the processing circuitry 1002. The system bus 1006 provides an interface for system components including, but not limited to, the memory 1004 and the processing circuitry 1002. The processing circuitry 1002 may include any number of hardware components for conducting data or signal processing or for executing computer code stored in memory 1004. The processing circuitry 1002 may, for example, include a general-purpose processor, an application specific processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a circuit containing processing components, a group of distributed processing components, a group of distributed computers configured for processing, or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. The processing circuitry 1002 may further include computer executable code that controls operation of the programmable device.
The system bus 1006 may be any of several types of bus structures that may further interconnect to a memory bus (with or without a memory controller), a peripheral bus, and/or a local bus using any of a variety of bus architectures. The memory 1004 may be one or more devices for storing data and/or computer code for completing or facilitating methods described herein. The memory 1004 may include database components, object code components, script components, or other types of information structure for supporting the various activities herein. Any distributed or local memory device may be utilized with the systems and methods of this description. The memory 1004 may be communicably connected to the processing circuitry 1002 (e.g., via a circuit or any other wired, wireless, or network connection) and may include computer code for executing one or more processes described herein. The memory 1004 may include non-volatile memory 1008 (e.g., read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), etc.), and volatile memory 1010 (e.g., random-access memory (RAM)), or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a computer or other machine with processing circuitry 1002. A basic input/output system (BIOS) 1012 may be stored in the non-volatile memory 1008 and can include the basic routines that help to transfer information between elements within the computer system 1000.
The computer system 1000 may further include or be coupled to a non-transitory computer-readable storage medium such as the storage device 1014, which may comprise, for example, an internal or external hard disk drive (HDD) (e.g., enhanced integrated drive electronics (EIDE) or serial advanced technology attachment (SATA)), HDD (e.g., EIDE or SATA) for storage, flash memory, or the like. The storage device 1014 and other drives associated with computer-readable media and computer-usable media may provide non-volatile storage of data, data structures, computer-executable instructions, and the like.
Computer-code which is hard or soft coded may be provided in the form of one or more modules. The module(s) can be implemented as software and/or hard-coded in circuitry to implement the functionality described herein in whole or in part. The modules may be stored in the storage device 1014 and/or in the volatile memory 1010, which may include an operating system 1016 and/or one or more program modules 1018. All or a portion of the examples disclosed herein may be implemented as a computer program 1020 stored on a transitory or non-transitory computer-usable or computer-readable storage medium (e.g., single medium or multiple media), such as the storage device 1014, which includes complex programming instructions (e.g., complex computer-readable program code) to cause the processing circuitry 1002 to carry out actions described herein. Thus, the computer-readable program code of the computer program 1020 can comprise software instructions for implementing the functionality of the examples described herein when executed by the processing circuitry 1002. In some examples, the storage device 1014 may be a computer program product (e.g., readable storage medium) storing the computer program 1020 thereon, where at least a portion of a computer program 1020 may be loadable (e.g., into a processor) for implementing the functionality of the examples described herein when executed by the processing circuitry 1002. The processing circuitry 1002 may serve as a controller or control system for the computer system 1000 that is to implement the functionality described herein.
The computer system 1000 may include an input device interface 1022 configured to receive input and selections to be communicated to the computer system 1000 when executing instructions, such as from a keyboard, mouse, touch-sensitive surface, etc. Such input devices may be connected to the processing circuitry 1002 through the input device interface 1022 coupled to the system bus 1006 but can be connected through other interfaces, such as a parallel port, an Institute of Electrical and Electronic Engineers (IEEE) 1394 serial port, a Universal Serial Bus (USB) port, an IR interface, and the like. The computer system 1000 may include an output device interface 1024 configured to forward output, such as to a display, a video display unit (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)). The computer system 1000 may include a communications interface 1026 suitable for communicating with a network as appropriate or desired.
FIG. 11 is a flow chart illustrating an example method 1100 which summarizes at least some of the above discussion. There is illustrated a computer-implemented method 1100 for controlling a propulsion system arranged in a marine vessel. The marine vessel comprises a drive unit that is adapted to drive a single propeller with a propeller pitch via a propeller axle. The steps of the method 1100 are carried out by processing circuitry of a computer system. The method 1100 comprises at 1110 determining a propeller slip of the single propeller based on an axle speed of the propeller axle, speed data indicative of a speed through water of the marine vessel, and the propeller pitch. The method 1100 comprises at 1120 determining a current yaw motion of the marine vessel based on angular velocity data obtained from at least one yaw motion sensor arranged on the marine vessel, the angular velocity data being indicative of a rotational movement of the marine vessel about a vertical axis. The method 1100 comprises at 1130 controlling an axle speed of the propeller axle based on a relationship between propulsion force generated by the drive unit and the propeller slip such that the propeller slip is maintained below a predetermined slip limit. The method 1100 comprises at 1140 controlling a steering angle of the drive unit based on a difference between the current yaw motion and a desired yaw motion.
FIG. 12 illustrates a computer readable medium 1210 carrying a computer program comprising program code means 1220 for performing the methods illustrated in FIG. 11 and the techniques discussed herein, when said program product is run on a computer. The computer readable medium and the code means may together form a computer program product 1200.
The operational actions described in any of the exemplary aspects herein are described to provide examples and discussion. The actions may be performed by hardware components, may be embodied in machine-executable instructions to cause a processor to perform the actions, or may be performed by a combination of hardware and software. Although a specific order of method actions may be shown or described, the order of the actions may differ. In addition, two or more actions may be performed concurrently or with partial concurrence.
Example 1: A computer system (120; 600; 1000) for controlling a propulsion system (105) arranged in a marine vessel (100), the propulsion system (105) comprising a drive unit (110) adapted to drive a single propeller (114) with a propeller pitch (P) via a propeller axle (112), the computer system (120; 600; 1000) comprising processing circuitry (122; 1002) configured to: determine a propeller slip (λ) of the single propeller (114) based on an axle speed (ω_P ) of the propeller axle (112), speed data indicative of a speed through water (v_W ) of the marine vessel (100), and the propeller pitch (P) determine a current yaw motion (ω_z ) of the marine vessel (100) based on angular velocity data obtained from at least one yaw motion sensor (150) arranged on the marine vessel (100), the angular velocity data being indicative of a rotational movement of the marine vessel (100) about a vertical axis; control an axle speed (ω_P ) of the propeller axle (112) based on a relationship between propulsion force generated by the drive unit (110) and the propeller slip (λ) such that the propeller slip (λ) is maintained below a predetermined slip limit (λ_lim ); and control a steering angle (δ_z ) of the drive unit (110) based on a difference between the current yaw motion (ω_z ) and a desired yaw motion (ω_zr ).
Example 2: The computer system (120; 600; 1000) according to Example 1, wherein the desired yaw motion (ω_zr ) is a user-requested propeller walk.
Example 3: The computer system (120; 600; 1000) of any preceding example, wherein the processing circuitry (122; 1002) is further configured to simultaneously control the axle speed (ω_P ) and the steering angle (δ_z ) such that the propeller slip (λ) is maintained below the predetermined slip limit (λ_lim ) and the steering angle (δ_z ) is controlled based on a difference between the current yaw motion (ω_z ) and a desired yaw motion (ω_zr ).
Example 4: The computer system (120; 600; 1000) of Example 3, wherein the processing circuitry (122; 1002) is further configured to: detect an operational condition of the marine vessel (100) indicating a conflict in said simultaneous control causing the propeller slip (λ) to violate the predetermined slip limits (λ_lim ) and/or failure of the steering angle (δ_z ) to be controlled based on said difference between the current yaw motion (ω_z ) and the desired yaw motion (ω_zr ); and in response to detecting said operational condition, prioritize control of the steering angle (δ_z ) over control of the propeller slip (λ).
Example 5: The computer system (120; 600; 1000) of Example 4, wherein the operational condition is a reduction in said speed through water (v_W ) exceeding a brake limit value.
Example 6: The computer system (120; 600; 1000) of any of Examples 4-5, wherein the operational condition is an increase in said speed through water (v_W ) exceeding an acceleration limit value.
Example 7: The computer system (120; 600; 1000) of any of Examples 4-6, wherein the operational condition is a direction change of the marine vessel (100) exceeding a directional change limit value.
Example 8: The computer system (120; 600; 1000) of any of Examples 4-7, wherein the operational condition is an adverse sea condition of an environment where the marine vessel (100) operates.
Example 9: The computer system (120; 600; 1000) of any of Examples 4-8, wherein the operational condition is an automatic collision avoidance maneuver of an automatic control functionality of the marine vessel (100).
Example 10: The computer system (120; 600; 1000) of any preceding example, wherein the desired yaw motion (ω_zr ) is obtained based on one or more of: a predefined navigational course determined by a route planner of the marine vessel (100), input from a user-operated control interface of the marine vessel (100), and a collision avoidance algorithm implemented by the computer system (120; 600; 1000).
Example 11: The computer system (120; 600; 1000) of any preceding example, wherein the propulsion system (105) is an electric propulsion system (105) and the drive unit (110) is an electric drive unit (110).
Example 12: The computer system (120; 600; 1000) of Example 11, wherein the electric drive unit (110) comprises an electric machine (111) arranged to provide a target axle speed for the propeller axle (112) upon request from the computer system (120; 600; 1000).
Example 13: The computer system (120; 600; 1000) according to any preceding example, wherein the processing circuitry (122; 1002) is configured to receive the speed data from a speed log (160) arranged on the vessel (100).
Example 14: The computer system (120; 600; 1000) according to any preceding example, wherein the processing circuitry (122; 1002) is configured to receive the speed data as speed over ground data from a global positioning system arranged on the vessel (100) and/or from a sonar sensor system.
Example 15: The computer system (120; 600; 1000) according to any preceding example, wherein the processing circuitry (122; 1002) is configured to determine the relationship between the propulsion force and the propeller slip (λ) at least in part as a predetermined analytical function or a collection of predetermined analytical functions.
Example 16: The computer system (120; 600; 1000) of Example 15, wherein the relationship between the propulsion force and the propeller slip (λ) is obtained from a preconfigured look-up table.
Example 17: The computer system (120; 600; 1000) of any preceding example, wherein the processing circuitry (122; 1002) is configured to: control a port side drive unit (810) and a starboard side drive unit (820); and configure a lower propeller slip limit ( $λ_{\lim}^{o}$ ) for an outer drive unit (820) out of the port side drive unit (810) and the starboard side drive unit (820) compared to a propeller slip limit ( $λ_{\lim}^{i}$ ) for an inner drive unit (810) out of the port side drive unit (810) and the starboard side drive unit (820).
Example 18: The computer system (120; 600; 1000) of any preceding example, wherein the drive unit (110) comprises an adjustable propeller pitch (P), and wherein the processing circuitry (122; 1002) is configured to control the axle speed (ω_P ) and the propeller pitch (P) to generate a target propeller slip (λ), based on a predetermined relationship (900) between efficiency, motor axle speed, and applied torque of an electric machine (111) of the drive unit (110).
Example 19: The computer system (120; 600; 1000) of any preceding example, comprising a centralized vessel motion management, VMM, module (620) arranged to request the desired yaw motion (ω_zr ) from at least one motion support device, MSD, control module (630).
Example 20: The computer system (120; 600; 1000) of any preceding example, comprising a centralized vessel motion management, VMM, module (130) arranged to request a propeller slip (λ) from at least one motion support device, MSD, control module (630).
Example 21: The computer system (120; 600; 1000) of any preceding example, comprising a centralized vessel motion management, VMM, module (130) arranged to request an axle speed (ω_P ) from at least one motion support device, MSD, control module (630).
Example 22: A propulsion system (105) arranged in a marine vessel (100), comprising: a drive unit (110) adapted to drive a single propeller (114) with a propeller pitch (P) via a propeller axle (112); and the computer system (120; 600; 1000) of any of Examples 1-21.
Example 23: A marine vessel (100) comprising: the computer system (120; 600; 1000) of any of Examples 1-21; and the propulsion system (105) of Example 22.
Example 24: A computer-implemented method (1100) for controlling a propulsion system (105) arranged in a marine vessel (100) and comprising a drive unit (110), the drive unit (110) being adapted to drive a single propeller (114) with a propeller pitch (P) via a propeller axle (112), the method (1100) comprising: determining (1110), by processing circuitry (122; 1002) of a computer system (120; 600; 1000), a propeller slip (λ) of the single propeller (114) based on an axle speed (ω_P ) of the propeller axle (112), speed data indicative of a speed through water (v_W ) of the marine vessel (100), and the propeller pitch (P); determining (1120), by the processing circuitry (122; 1002), a current yaw motion (ω_z ) of the marine vessel (100) based on angular velocity data obtained from at least one yaw motion sensor (150) arranged on the marine vessel (100), the angular velocity data being indicative of a rotational movement of the marine vessel (100) about a vertical axis; controlling (1130), by the processing circuitry (122; 1002), an axle speed (ω_P ) of the propeller axle (112) based on a relationship between propulsion force generated by the drive unit (110) and the propeller slip (λ) such that the propeller slip (λ) is maintained below a predetermined slip limit (λ_lim ); and controlling (1140), by the processing circuitry (122; 1002), a steering angle (δ_z ) of the drive unit (110) based on a difference between the current yaw motion (ω_z ) and a desired yaw motion (ω_zr ).
Example 25: A computer program product (1200) comprising program code for performing, when executed by processing circuitry (122; 1002), the method of Example 24.
Example 26: A non-transitory computer-readable storage medium (1210) comprising instructions, which when executed by processing circuitry (122; 1002), cause the processing circuitry (122; 1002) to perform the method of Example 24.
The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms "comprises," "comprising," "includes," and/or "including" when used herein specify the presence of stated features, integers, actions, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, actions, steps, operations, elements, components, and/or groups thereof.
It will be understood that, although the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the present disclosure.
Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe a relationship of one element to another element as illustrated in the figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
It is to be understood that the present disclosure is not limited to the aspects described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the present disclosure and appended claims. In the drawings and specification, there have been disclosed aspects for purposes of illustration only and not for purposes of limitation, the scope of the disclosure being set forth in the following claims

Claims

A computer system (120; 600; 1000) for controlling a propulsion system (105) arranged in a marine vessel (100), the propulsion system (105) comprising at least one drive unit (110) adapted to drive a respective single propeller (114) with a propeller pitch (P), via a propeller axle (112), the computer system (120; 600; 1000) comprising processing circuitry (122; 1002) configured to:
determine a propeller slip (λ) of the single propeller (114) based on an axle speed (ω_P ) of the propeller axle (112), speed data indicative of a speed through water (v_W ) of the marine vessel (100), and the propeller pitch (P);

determine a current yaw motion (ω_z ) of the marine vessel (100) based on angular velocity data obtained from at least one yaw motion sensor (150) arranged on the marine vessel (100), the angular velocity data being indicative of a rotational movement of the marine vessel (100) about a vertical axis;

control an axle speed (ω_P ) of the propeller axle (112) based on a relationship between propulsion force generated by the drive unit (110) and the propeller slip (λ) such that the propeller slip (λ) is maintained below a predetermined slip limit (λ_lim ); and

control a steering angle (δ_z ) of the drive unit (110) based on a difference between the current yaw motion (ω_z ) and a desired yaw motion (ω_zr ).
The computer system (120; 600; 1000) according to claim 1, wherein the desired yaw motion (ω_zr ) is a user-requested propeller walk.
The computer system (120; 600; 1000) of any preceding claim, wherein the processing circuitry (122; 1002) is further configured to simultaneously control the axle speed (ω_P ) and the steering angle (δ_z ) such that the propeller slip (λ) is maintained below the predetermined slip limit (λ_lim ) and the steering angle (δ_z ) is controlled based on a difference between the current yaw motion (ω_z ) and a desired yaw motion (ω_zr ).
The computer system (120; 600; 1000) of claim 3, wherein the processing circuitry (122; 1002) is further configured to:
detect an operational condition of the marine vessel (100) indicating a conflict in said simultaneous control causing the propeller slip (λ) to violate the predetermined slip limits (λ_lim ) and/or failure of the steering angle (δ_z ) to be controlled based on said difference between the current yaw motion (ω_z ) and the desired yaw motion (ω_zr ); and

in response to detecting said operational condition, prioritize control of the steering angle (δ_z ) over control of the propeller slip (λ).
The computer system (120; 600; 1000) of claim 4, wherein the operational condition is a reduction in said speed through water (v_W ) exceeding a brake limit value.
The computer system (120; 600; 1000) of any of claims 4-5, wherein the operational condition is an increase in said speed through water (v_W ) exceeding an acceleration limit value.
The computer system (120; 600; 1000) of any of claims 4-6, wherein the operational condition is a direction change of the marine vessel (100) exceeding a directional change limit value.
The computer system (120; 600; 1000) of any of claims 4-7, wherein the operational condition is an adverse sea condition of an environment where the marine vessel (100) operates.
The computer system (120; 600; 1000) of any preceding claim, wherein the desired yaw motion (ω_zr ) is obtained based on one or more of:
a predefined navigational course determined by a route planner of the marine vessel (100),

input from a user-operated control interface of the marine vessel (100), and

a collision avoidance algorithm implemented by the computer system (120; 600; 1000).
The computer system (120; 600; 1000) of any preceding claim, comprising a centralized vessel motion management, VMM, module (620) arranged to request the desired yaw motion (ω_zr ) from at least one motion support device, MSD, control module (630).
A propulsion system (105) arranged in a marine vessel (100), comprising:
a drive unit (110) adapted to drive a single propeller (114) with a propeller pitch (P) via a propeller axle (112); and

the computer system (120; 600; 1000) of any of claims 1-10.
A marine vessel (100) comprising:
the computer system (120; 600; 1000) of any of claims 1-10; and

the propulsion system (105) of claim 11.
A computer-implemented method (1100) for controlling a propulsion system (105) arranged in a marine vessel (100) and comprising at least one drive unit (110), the drive unit (110) being adapted to drive a respective single propeller (114) with a propeller pitch (P) via a propeller axle (112), the method (1100) comprising:
determining (1110), by processing circuitry (122; 1002) of a computer system (120; 600; 1000), a propeller slip (λ) of the single propeller (114) based on an axle speed (ω_P ) of the propeller axle (112), speed data indicative of a speed through water (v_W ) of the marine vessel (100), and the propeller pitch (P);

determining (1120), by the processing circuitry (122; 1002), a current yaw motion (ω_z ) of the marine vessel (100) based on angular velocity data obtained from at least one yaw motion sensor (150) arranged on the marine vessel (100), the angular velocity data being indicative of a rotational movement of the marine vessel (100) about a vertical axis;

controlling (1130), by the processing circuitry (122; 1002), an axle speed (ω_P ) of the propeller axle (112) based on a relationship between propulsion force generated by the drive unit (110) and the propeller slip (λ) such that the propeller slip (λ) is maintained below a predetermined slip limit (λ_lim ); and

controlling (1140), by the processing circuitry (122; 1002), a steering angle (δ_z ) of the drive unit (110) based on a difference between the current yaw motion (ω_z ) and a desired yaw motion (ω_zr ).
A computer program product (1200) comprising program code for performing, when executed by processing circuitry (122; 1002), the method of claim 13.
A non-transitory computer-readable storage medium (1210) comprising instructions, which when executed by processing circuitry (122; 1002), cause the processing circuitry (122; 1002) to perform the method of claim 13.