Patent Description:
The maintenance schedules of engine components are often based on engine running hours and lack any indication of the actual wear and functionality of the components. Condition-based maintenance (CBM) is an improvement of this maintenance approach, in which maintenance schedules are based on the evaluation of the deviation from standard values using trends and statistical parameters (e.g. limits, thresholds based on experience). However, these parameters cannot be set without clear knowledge of the components and experience of previous failures.

<CIT> discloses fault detection and response techniques using an operational signature generated based on sensor signals from sensors operatively coupled to an engine system.

<CIT> discloses a piston engine and an arrangement for detecting a failure of a head gasket of the piston engine by monitoring pressure of cooling liquid and torsional vibrations of a crankshaft.

<CIT> discloses a failure prediction device for an internal combustion engine. Values obtained from a plurality of sensors are compared to reference values to determine abnormality.

<CIT> discloses a method for sensing damage of bearing of engine using a vibration signal.

According to a first aspect of the invention, a computer-implemented method for estimating a condition of at least one engine component in a piston engine is provided in claim <NUM>.

Estimating the condition of the at least one component may be done in real-time.

The method may comprise estimating the condition of more than one component.

The mechanical system may be an internal combustion engine, such as a four-stroke engine.

The sensor signals may include one or more of: internal combustion pressure, receiver air pressure, receiver air temperature, exhaust gas pressure, exhaust gas temperature, engine load and engine speed.

Calculating torsional vibration response of the at least one component may comprise calculating the torsional vibration response at multiple positions on the component. At least one of the positions on the component may be a position that is not directly connected to a sensor.

Inputting the calculated torsional vibration response of the at least one component into a cumulative damage model may comprise inputting the torsional vibration stress history of the at least one component into the cumulative damage model.

The cumulative damage model may comprise rainflow counting of the torsional vibration stress history in order to determine the cumulative number of cycles of stress at each of a plurality of stress levels and applying Miner's rule to the cumulative number of cycles of stress to calculate the cumulative damage.

The method may further comprise providing a maintenance request when the cumulative damage exceeds a first threshold.

The method may further comprise providing a warning or alarm when the cumulative damage exceeds a second threshold.

The method may further comprise estimating the residual lifetime of the at least one component based on the cumulative damage model.

The method may further comprise outputting the residual lifetime of the at least one component.

According to a second aspect of the invention, a system may be provided, the system comprising a processor configured to perform the method as described above.

According to a third aspect of the invention, a computer program may be provided, the computer program comprising instructions which, when the program is executed by a processor, causes a computer to perform the method described above.

According to a fourth aspect of the invention, a non-transitory computer readable medium is provided, the computer readable medium comprising instructions which, when the program is executed by a processor, causes a computer to perform the method described above.

The present invention solves the problems associated with running hours-based and conventional condition-based maintenance of an engine by using a torsional vibration model of the engine in order to accurately calculate the torsional vibration response of components within the engine based on real and simulated sensor data. The torsional vibration response is input into a cumulative damage model of the component, which may be used directly to indicate when maintenance is required (e.g. which the cumulative damage crosses a threshold) and alternatively, or additionally, may be used to estimate the residual lifetime of the component.

While the description of the invention herein is primarily in the context of engines, it will be appreciated that the invention itself is more general and can be applied to any mechanical system, being based on a torsional vibration model of that system.

A torsional vibration model is a numerical model created to simulate the torsional vibration of mechanical components - in the case of an engine, typically the crankshaft and connected components. More information regarding torsional vibration models and their use in engine design can be found, for example, in "<NPL>. Torsional vibration models are produced during the design phase of engine development; however, following the design phase, the torsional vibrational model is generally no longer used. However, in the present invention, the torsional vibration model is advantageously used to determine the torsional vibration of engine components based on real-world sensor data while the engine is operating.

<FIG> shows part of an exemplary engine <NUM>, the condition of which may be monitored by the method of the present invention. The engine <NUM> includes a crankshaft <NUM>, which is made up of a series of cranks that are connected to the pistons of the engine cylinder or cylinders. The crankshaft <NUM> converts the reciprocating motion of the piston to rotational motion. The crankshaft <NUM> may also be connected to a flywheel in order to reduce the effect of pulsation in the engine cylinder cycle, and to a vibration damper in order to reduce torsional vibration of the crankshaft <NUM>. The engine <NUM> also includes a coupling <NUM>, which couples the rotational motion of the crankshaft to another component outside of the engine, e.g. a generator. The coupling <NUM> is formed from rubber or a similar material, such as silicone, in order to account for misalignments that are the result of manufacturing tolerances and to reduce transmission of torsional vibration from the crankshaft to the component outside the engine. The energy dissipated in the reduction of transmission of torsional vibration is transformed in heat inside the coupling material during engine operation. Therefore, in addition to the torsional vibration stress itself, which may negatively affect the condition of the coupling <NUM>, heating of the coupling <NUM> during engine operation can also negatively affect the condition of the coupling <NUM>. Also shown in <FIG> are a flywheel <NUM> and generator shaft <NUM>, which transmits power from the engine <NUM> to further components, such as a propeller, vehicle drivetrain and/or electrical generator.

<FIG> is an exemplary schematic drawing of the torsional vibration model of engine <NUM> shown in <FIG>. Elements <NUM>-<NUM> correspond to the crankshaft <NUM> and engine components (such as engine cylinders), element <NUM> corresponding to the flange/flywheel <NUM>, and elements <NUM>-<NUM> correspond to the coupling <NUM>. The individual numbered elements shown in <FIG> are as follows:.

<FIG> shows a method for estimating the condition of at least one mechanical component in a mechanical system, such as an engine. The at least one mechanical component may be the crankshaft <NUM> or the coupling <NUM>, or the method may be used to estimate the condition of both the crankshaft and coupling <NUM> at the same time, for example. The method is performed on a computer and is implemented as a software programme that runs on the computer. The software, and the computer, may interact with other components external to the computer, such as sensors or other input devices, and output devices such as loudspeakers, displays or alarms.

At step <NUM>, the torsional vibration model is obtained. The model may be obtained from a memory of the computer, or may be obtained over a network connection from another computer, for example. As explained above, the torsional vibration model is a model of the torsional vibration properties of the at least one component whose condition is being estimated. The torsional vibration model takes as input engine automation signals, such as the internal cylinder pressure of each cylinder, engine speed, engine air pressure, engine temperature, receiver air pressure, receiver temperature, exhaust gas temperature and exhaust gas pressure. The torsional vibration model may take any combination of these signals as inputs. The torsional vibration model outputs the torsional vibration stress of the component, of sub-sections of the component, or at different points within the component. Where the component is the crankshaft <NUM>, the torsional vibration model is used to determine the torsional vibration stress at different points along the crankshaft, including at positions where it is impossible to place sensors to directly measure the state and condition of the crankshaft. Where the component is the coupling <NUM>, the torsional vibration model may also output the torsional vibration stress, along with the angular deflection, vibratory torque, power loss and/or temperature of the coupling <NUM>. Any combination of the outputs lists above may be produced by the torsional vibration model.

At step <NUM>, sensor signals are acquired from sensors installed on or otherwise connected to or in communication with the mechanical system. The sensors from which signals are acquired include those suitable for measuring the torsional vibration model input models mentioned above, i.e. the internal cylinder pressure of each cylinder, engine speed, engine air pressure, engine temperature, receiver air pressure, receiver temperature, exhaust gas temperature and/or exhaust gas pressure. Any combination of the sensors may be provided and used in the system to provide the required sensor signals.

At step <NUM>, the torsional vibration response of the component is calculated based on the torsional vibration model and the acquired sensor signals. In this context, the term "torsional vibration response" means any of the quantities listed above which depend on or are related to the torsional vibration of the system and may be provided as outputs of the model, i.e. torsional vibration stress, angular deflection, vibratory torque, power loss and/or temperature of the component. The torsional vibration response calculated from the model may include any combination of these quantities. The torsional vibration model can therefore be considered to produce simulated sensor signals relating to these torsional vibration response quantities at positions or on components that are impossible to install sensors on.

At step <NUM>, the torsional vibration response - i.e. the simulated sensor signals - are used to estimate the condition of the component. A cumulative damage model is used to estimate the condition of the component. For torsional vibration stress, the stress time history, i.e. the calculated torsional vibration stress over time, is analysed using the rainflow-counting algorithm to identify torsional vibration stress cycles of the component. More information about rainflow-counting can be found in <NPL>. Where the component is the crankshaft <NUM>, this analysis may be performed at a single location on the crankshaft <NUM> (e.g. a stress hotspot or other location known to be subject to the large stress) or at multiple locations on the crankshaft <NUM>. This provides a breakdown of the number of cycles of stress at different stress intervals. The cumulative damage is then calculated using Miner's rule, which states that the damage D, is given by the following equation: <MAT> where ni is the number of cycles accumulated at a given stress interval Si and Ni is the number of cycles at the given stress interval Si at which the component fails. The number Ni may be calculated experimentally, e.g. based on a S-N curve, which plots the cyclic stress S against the cycles to failure N. When the damage D equals <NUM>, failure of the component is indicated.

Where the estimation of the condition of the component is done in real-time, the number of cycles of stress at each interval are updated in real-time based on the output of the torsional vibration model, which itself receives input from the sensors in real time. The cumulative damage D, calculated according to the equation above, is then updated based on the updated number of stress cycles.

When the cumulative damage D exceeds a threshold, a warning may be provided, e.g. on a display in a GUI associated with the condition monitoring process, indicating that the component may need to be serviced or replaced soon. If the cumulative damage exceeds a second, higher threshold, an alarm, e.g. an audio and/or visual alarm, may be provided indicating that failure of the component is imminent.

Where the component is the coupling <NUM>, the following method may be followed:.

The steps above are then repeated at subsequent time steps while the engine is in operation in order to monitor the state and condition of the coupling over time. The steps above can be performed in real-time as new sensor data is acquired for the torsional vibration model and as new temperatures for the rubber coupling are calculated.

A convergence criterion is set on temperature difference between adjacent time steps (or alternatively on dissipation energy) which define a maximum temperature difference δ between time steps. The maximum temperature difference may be, for example, <NUM> C. The convergence criterion ensures stability of the model. Furthermore, since the calculation process describe above is an iterative process, the convergence ensures that the process passes to the next step with an acceptable and accurate calculation precision.

If the calculated temperature difference exceeds the convergence criterion, the calculation continues the iterations as described above until the convergence criterion is satisfied.

The steps above are then repeated at subsequent engine cycle while the engine is in operation in order to monitor the state and condition of the coupling over time. The steps above can be performed in real-time as new sensor data is acquired for the torsional vibration model and as new temperatures for the rubber coupling are calculated.

In addition, a monitoring system alarm and warning may be implemented based on the temperature of the coupling. For example, the maximum permissible coupling core temperature is <NUM> for natural rubber and <NUM> for silicone.

Other advanced control can be implemented; for example, the temperature increment per hour can be monitored and it should be almost constant in steady state condition. In the event of a quickly increasing temperature, a warning alarm is displayed. For example, a warning may be issued if ΔTemp > <NUM>/h.

At an optional step <NUM>, the residual lifetime of the engine component or components is calculated. Residual lifetime may be calculated as described in <NPL>.

In general, the steps of the method described above may be performed in real-time in order to maintain an accurate model of the condition and damage of the components. As such, a "digital twin" of the engine may be maintained in the memory of the computer.

<FIG> shows a system for monitoring the condition of a mechanical system according to the present invention. Engine <NUM> is the engine described above with respect to <FIG> and monitored by the method described with respect to and shown in <FIG>. The engine may be the engine of a marine vessel or power plant, for example.

The engine <NUM> is monitored and controlled by engine automation system <NUM> (e.g. engine automation system <NUM> shown in <FIG>). Engine automation system <NUM> may be an automation system such as a UNIC engine automation system, which is a modular, embedded control system for control and monitoring of diesel and gas engines developed by Wärtsilä®. A UNIC system facilitates fundamental engine safety functions, engine monitoring and control of fuel injection and ignition functionalities. The system also includes start/stop logics and speed/load control. The engine automation system <NUM> gathers the necessary sensor data for the torsional vibration model described above. As such, the system may include a plurality of sensors located on or in engine <NUM>.

The system also includes one or more of a local control apparatus <NUM> and a remote control apparatus <NUM>. The method described above with respect to <FIG> is preferably implemented as software on the local control apparatus <NUM> or remote control apparatus <NUM>, taking advantage of the existing engine sensors that are part of the engine automation system. However, in some embodiments, the engine automation system <NUM> may not be present and instead the local control apparatus <NUM> or remote control apparatus <NUM> may be connected to other sensors that are part of the engine <NUM>. The local control apparatus <NUM> and/or remote control apparatus <NUM> is configured to generate maintenance request once the residual lifetime of the engine component or calculated engine component damage exceeds a threshold. The remote control apparatus <NUM> may be connected directly to the engine automation system <NUM> via a network, such as the internet, or may instead connect to the local control apparatus <NUM>, when both are provided.

In an embodiment, the local control apparatus <NUM> and/or remote control apparatus <NUM> is configured to generate maintenance request based on the residual lifetime of the engine component or calculated engine component damage combined with predicted operation schedule.

The predicted operation schedule may comprise, for example, forthcoming route information of future voyages of a marine vessel or predicted environmental information of a power plant utilising an engine as a backup power source for wind or solar, for example.

By combining the improved estimation of a component's condition and the predicted operation schedule, the service of the component may be further optimised. For a marine vessel, an optimal location, dock and time may be determined for the service, for example. For a power plant, an optimal time when there is forecasted wind and/or solar energy available, may be determined. Energy storages may be utilised for temporary backup and peak-shaving as well.

Claim 1:
A computer-implemented method for estimating a condition of at least one engine component in a piston engine having a crankshaft converting reciprocating motion of pistons to rotational motion, wherein the at least one engine component comprises at least one of the crankshaft and crankshaft rubber couplings, the method comprising:
obtaining a torsional vibration model of the at least one engine component;
acquiring sensor signals from sensors installed on the piston engine;
calculating torsional vibration response of the at least one engine component based on the acquired sensor signals and the torsional vibration model, wherein the torsional vibration response means quantities which depend on or are related to the torsional vibration of the piston engine and are provided as outputs of the model, wherein the calculating torsional vibration response of the at least one engine component comprises i) calculating the torsional vibration response at multiple positions on the engine component, and wherein at least one of the positions on the engine component is a position that is not directly connected to a sensor, or ii) calculating torsional vibration response of at least one engine component on which sensors cannot be installed; and
estimating the condition of the at least one engine component by inputting the calculated torsional vibration response of the at least one engine component into a cumulative damage model of the engine component, wherein inputting the calculated torsional vibration response of the at least one engine component into the cumulative damage model comprises inputting a torsional vibration stress history of the engine component into the cumulative damage model.