Two-stroke engine with lubrication failure detection

Abstract

The crankcase scavenging two-stroke engine (200, 900) comprises a cylinder wall (260) having an intake port (250) and an exhaust port (251), and is associated with an idle operating mode and an active operating mode, the speed (ω) of the engine (200, 900) being faster in the active operating mode than in the idle operating mode, and the engine (200, 900) comprises at least one engine vibration sensor (270) configured to sense vibrations from the engine (200, 900) and output an engine vibration signal (275), and a control unit (280) configured to detect insufficient lubrication in the engine (200, 900) based on the engine vibration signal (275).

Description

Technical Field

[0001] The present disclosure relates to hand-held power tools such as wall saws, electric cutters, and chain saws, and construction machinery. A crankcase scavenged two-stroke engine, a vibration sensor device, a control unit, and a method for detecting insufficient lubrication of a combustion engine and mitigating the effects of insufficient engine lubrication are disclosed. Some aspects of the present disclosure relate to the detection of other faults such as a damaged air filter.

Background Art

[0002] Most combustion engines require some form of lubrication system to operate properly. More advanced combustion engines, such as four-stroke engines, often have a separate oil pump to provide the necessary lubrication. Insufficient lubrication in a combustion engine is undesirable because it can lead to overheating, increased fuel consumption, and ultimately piston seizure.

[0003] Patent Document 1 discloses a combustion engine provided with a control unit configured to control an oil pump based on the sensed vibration of the combustion engine.

[0004] Patent Document 2 relates to an automatic oil supply device controlled based on the temperature or vibration sensed by a combustion engine.

[0005] Patent Document 3 describes a piston protection system for a two-stroke engine based on vibration data obtained from a vibration sensor.

[0006] There is a need for a less complex method for detecting insufficient lubrication suitable for smaller crankcase scavenged two-stroke engines. An improvement in detection reliability is also desired.

[0007] Furthermore, there is a need for a cost-effective manufacturing method for producing the components desirable for implementing the less complex method for detecting insufficient lubrication described above. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] U.S. Patent No. 10900393 [Patent Document 2] Swiss Patent Application Publication No. 613495 [Patent Document 3] U.S. Patent No. 5062399 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The object of this disclosure is to provide engines, sensors, and sensor systems for detecting insufficient lubrication in small crankcase scavenging two-stroke engines of the type used in handheld power tools and small construction machinery such as floor saws. At least some of the sensors and sensor systems disclosed herein are limited in complexity and do not require processing circuits with considerable computing power. [Means for solving the problem]

[0010] The above objective is at least partially achieved by a crankcase scavenging two-stroke engine having a cylinder wall having at least one intake port and at least one exhaust port. The engine is associated with an idle operating mode and an active operating mode, with the engine speed being faster in the active operating mode than in the idle operating mode. The engine is typically in the active operating mode when the power tool driven by the engine is actively used to perform a work task, and in the idle operating mode when the power tool is not actively used. The engine is equipped with at least one engine vibration sensor configured to sense engine vibrations and output an engine vibration signal. The engine also includes, or is associated with, a control unit configured to detect lubrication deficiencies in the engine based on engine vibration signals in at least one delimited frequency band, such as a predetermined frequency band. The delimited frequency bands can be a low-pass band delimited by the highest frequency, a high-pass band delimited by the lowest frequency, or frequency bands delimited by low-end and high-end frequencies. It has been found that lubrication deficiencies exhibit different vibration signatures in different frequency bands. For example, the amplitude of vibrations at low frequencies may decrease, while the amplitude of vibrations at higher frequencies may increase due to the same lubrication deficiency. Therefore, monitoring the engine vibration signal in at least one delimited frequency band, such as a low-frequency band and / or a high-frequency band, provides a more robust detection of engine lubrication deficiency compared to a lubrication deficiency detection system that does not limit the frequency band.

[0011] It is preferable that the detection of lubrication deficiency by the control unit also requires that the engine be in an active operating mode, i.e., that the engine is not operating in idle mode. This method of detecting lubrication deficiency is advantageous because the vibration characteristics of an engine indicating lubrication deficiency become more pronounced at higher engine speeds, at least in crankcase scavenging two-stroke engines, and it allows for a less complex detection mechanism compared to, for example, continuously adapting the lubrication deficiency detection algorithm to the current engine speed, as done in Patent Document 3. Attempting to detect lubrication deficiency at engine speeds that are too low, such as during idling, can lead to a significant number of false positives, even if the detection threshold is adapted to the current engine speed. In other words, according to some aspects of this specification, lubrication deficiency is detected only based on vibration data collected during high-speed engine operation, and not based on vibration data collected during low-speed operation such as idling. In this way, the number of false positives, i.e., the number of times lubrication deficiency is detected when there is actually no lubrication deficiency, can be significantly reduced.

[0012] An active operating mode can be defined as an engine operation when the engine speed exceeds a threshold or some other engine speed-dependent acceptance criterion, such as when the trigger or throttle leaves the standby or default position. Engine vibration signals can also be weighted by engine speed so that engine vibration data collected during high-speed engine operation is given more weight than engine vibration data collected during low-speed operation.

[0013] The control unit can be configured to be powered by a Peltier element mounted on the engine, which has the advantage of not requiring a dedicated power supply. Some aspects of the present disclosure also relate to a vibration sensor powered by the engine's ignition system, for example, by an ignition module mounted on the engine. According to some aspects, the vibration sensor is integrated into the engine's ignition module, enabling the cost-effective manufacture of a power tool including the engine and the engine vibration sensor.

[0014] Engine vibration sensors are preferably positioned connected to ports within the cylinder wall, such as the intake or exhaust ports of the engine. Engine vibration sensors can also be positioned directly connected to, for example, the engine's scavenging passages connecting the engine's crankcase to the cylinders, or to the engine's exhaust passages through which exhaust gases are ventilated from the cylinders, in which case particularly relevant vibration signals are generated in cases of insufficient lubrication. Some engines include scavenging passages, which are partially separated by covers. Mounting vibration sensors on such covers is advantageous.

[0015] At least one engine vibration sensor may include a piezoelectric element, such as a piezoelectric ceramic element. This type of vibration sensor is low-cost and robust. Two or more piezoelectric elements can be arranged in different directions to provide two-dimensional or three-dimensional vibration data. In other words, the vibration sensor may be a one-dimensional sensor arranged to sense engine vibrations in one dimension. However, using two-dimensional or three-dimensional sensors to sense engine vibrations can improve the system. High-dimensional vibration data is particularly well-suited for machine learning-based algorithms for lubrication deficiency detection, i.e., detection methods that are at least partially based on artificial intelligence (AI).

[0016] In a preferred embodiment, the control unit is configured to detect lubrication deficiency in the engine based on a decrease in vibration amplitude in a first frequency band below 20 kHz, preferably below 15 kHz. This behavior, where vibration amplitude decreases as a result of lubrication deficiency, is a characteristic of crankcase scavenging two-stroke engines and allows for efficient and reliable detection of lubrication deficiency at an early stage before piston seizure or other more serious effects resulting from lubrication deficiency occur. Vibration amplitude can be measured, for example, as the root-mean-square (RMS) value of vibration amplitude over a time window, or as the squared value after some kind of low-pass filtering. The first frequency band can include frequencies above 5 Hz, preferably above about 10 Hz, and up to about 15 kHz. The control unit may also be configured to detect lubrication deficiency in the engine based on an increase in engine vibration amplitude in a second frequency band above 50 kHz, preferably above 100 kHz, and up to about 450 kHz. This increase in vibration amplitude is more commonly observed in other types of engines, as shown in some of the relevant literature mentioned above. The ability to use two different mechanisms to detect lubrication deficiency is an advantage. Some lubrication deficiencies manifest better as a decrease in the amplitude of low-frequency vibrations, while others manifest as a more pronounced increase in the amplitude of high-frequency vibrations. The second frequency band can include frequencies below 500 kHz, preferably below approximately 450 kHz. This dual-band detection principle provides more robust detection of lubrication deficiency in crankcase-scavenging two-stroke engines compared to systems that use only one frequency band for detection.

[0017] Since insufficient lubrication affects vibration characteristics differently depending on the monitored frequency band, it is advantageous for the control unit to be configured to detect engine lubrication deficiency based on engine vibration signals in at least one delimited frequency band.

[0018] The control unit can be configured to detect lubrication deficiencies in the engine based on various principles, such as classical thresholding techniques, various statistical tests, and machine learning functions, as will be described in detail below.

[0019] It is advantageous for an engine to have multiple engine vibration sensors, connected to the cylinder walls and positioned at different locations, to sense each vibration produced by the engine. This allows the control unit to more accurately understand the engine's operating condition and more reliably detect lubrication deficiencies. The control unit can also use data from multiple vibration sensors mounted at different locations around the engine to infer and / or predict other types of abnormalities in the engine, which is an advantage. These other types of failures include, for example, a damaged or defective intake filter, a damaged crankshaft, and damage to power tools driven by the engine, such as a damaged saw blade or a damaged drill bit.

[0020] In some embodiments, the control unit is configured to receive data indicating external vibrations generated by an external source. In this case, the control unit can be configured to detect engine lubrication deficiency based on a combination of sensed engine vibrations and external vibrations. The control unit can use the data indicating external vibrations to suppress undesirable distortions in the engine vibration signal generated by vibrations of an engine-driven tool, such as a saw blade.

[0021] In some embodiments, the control unit is configured to limit the maximum engine speed or prevent engine operation in response to the detection of insufficient lubrication. In this way, the control unit can prevent more serious damage to the engine as a result of the detected insufficient lubrication. Engine speed control can be efficiently implemented through control of the spark plug operation if the insufficient lubrication system is integrated into the engine's ignition module.

[0022] The control unit can also control the variable oil distribution system in response to the detection of insufficient lubrication and is configured to increase the amount of oil distributed in response to the detection of insufficient lubrication. An oil reservoir for lubricating the engine can be provided, for example, connected to the engine and used on demand to provide lubrication as needed, which reduces the amount of oil required to operate the engine. The oil reservoir can be a sealed oil reservoir without an oil filling opening. Next, this sealed oil reservoir is sized to contain an amount of oil that will last for the expected life of the power tool driven by the engine. This means that the operator does not need to worry about replenishing or monitoring the oil level in the oil reservoir, which is an advantage.

[0023] Also, a crankcase scavenged two-stroke engine includes a cylinder wall having an intake port and an exhaust port, a spark plug, and an ignition module fixedly attached to the motor block of the engine and electrically connected to the spark plug. The engine includes an engine vibration sensor arranged to sense vibrations by the engine and output an engine vibration signal. The engine also includes a control unit configured to detect insufficient lubrication in the engine based on the engine vibration signal. The engine vibration sensor is integrated with the ignition module of the crankcase scavenged two-stroke engine. The control unit can also be integrated with the ignition module. This particular arrangement of the vibration sensor has at least two advantages. The ignition module is typically directly attached to the motor block and thus receives relatively weak vibrations generated by the interaction of the piston and cylinder with sufficient amplitude during insufficient lubrication. The ignition module also generates power for driving the spark plug. This power can be used to supply power to the vibration sensor and optionally also to the control unit. Also, by integrating the vibration sensor system and the ignition module, the insufficient lubrication detection system can be incorporated into various power tools in a cost-effective manner.

[0024] An ignition module equipped with an engine vibration sensor and a control unit according to the teachings of this specification can also directly control the engine speed by adjusting the operation of the spark plug according to the vibration signal. The engine speed can be reduced, for example, by reducing the amount of spark generated over a time window.

[0025] The present disclosure also relates to a crankcase scavenged two-stroke engine having a cylinder wall with an intake port and an exhaust port. The engine includes at least one engine vibration sensor arranged to sense vibrations by the engine and output an engine vibration signal, and a control unit configured to detect insufficient lubrication of the engine based on the engine vibration signal. The control unit is configured to detect insufficient lubrication of the engine based on a decrease in the amplitude of vibrations in a first frequency band and an increase in the amplitude of engine vibrations in a second frequency band above the first frequency band.

[0026] Also, as will be described below, various methods and technical features that can be used in an independent manner are also disclosed herein.

[0027] In general, all terms used in the claims should be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise in this specification. All references to "element, apparatus, component, means, step, etc." should be construed openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein need not be performed in the exact order disclosed, unless explicitly stated. Further features and advantages of the present invention will become apparent by considering the appended claims and the following description. Those skilled in the art will understand that they can combine different features of the present invention to create embodiments other than those described below without departing from the scope of the present invention.

[0028] The present disclosure will be described in more detail below with reference to the attached drawings. [Brief explanation of the drawing]

[0029] [Figure 1] Examples of handheld power tools are shown. [Figure 2] A schematic diagram of a two-stroke engine is shown. [Figure 3A] This shows vibrations caused by the piston ring passing through ports in the cylinder wall. [Figure 3B] This shows vibrations caused by the piston ring passing through ports in the cylinder wall. [Figure 4A] This is a graph showing the amplitude-time relationship of vibrations. [Figure 4B] This is a graph showing the amplitude-time relationship of vibrations. [Figure 5] This is a block diagram showing signal processing functions. [Figure 6] This is a flowchart illustrating an exemplary method. [Figure 7] An example of an engine vibration sensor is shown. [Figure 8] This flowchart shows a method for manufacturing an engine vibration sensor. [Figure 9A] An exemplary two-stroke engine with an ignition module is shown. [Figure 9B] An exemplary two-stroke engine with an ignition module is shown. [Figure 10] A schematic diagram of the piezoelectric vibration sensor configuration is shown below. [Figure 11] This is a diagram showing a three-dimensional vibration sensor. [Figure 12] An exemplary control unit including processing circuits is shown. [Modes for carrying out the invention]

[0030] The present invention will be described more fully below with reference to the accompanying drawings illustrating several aspects of the invention. However, the present invention can be carried out in many different forms and should not be construed as being limited to the embodiments and aspects described herein, but rather these embodiments are provided as examples so that the present disclosure is sufficient and complete and so as to convey the scope of the invention to those skilled in the art. Similar reference numerals refer to similar elements throughout the description.

[0031] It should be understood that the present invention is not limited to the embodiments described herein and shown in the drawings, and rather, those skilled in the art will recognize that many changes and modifications can be made within the scope of the appended claims.

[0032] Figure 1 shows an exemplary handheld power tool 100, in this case an electric cutter that can be used to cut hard materials such as concrete and stone. This type of handheld power tool is often driven by a crankcase scavenging two-stroke engine 110 that provides a high power-to-weight ratio. This disclosure relates to lubrication in crankcase scavenging two-stroke engines of a type commonly used in electric cutting machines, chainsaws, leaf blowers, cleaning saws, and other handheld power tools. Some of the techniques described herein can also be used in lightweight construction equipment such as floor saws.

[0033] Figure 2 schematically shows an exemplary crankcase scavenging two-stroke engine 200. The engine 200 comprises a piston 210 that reciprocates within a cylinder 220, which also comprises a spark plug 230 or other ignition means in a known manner. The reciprocating motion of the piston 210 causes a crankshaft 245, housed in a crankcase 240, to rotate at an engine speed ω.

[0034] The engine speed ω is controlled by a trigger 120 connected to the throttle device of engines 110 and 200. The engine speed can be determined directly using an engine speed sensor, such as a Hall effect element or rotary encoder, located on or connected to the engine drive shaft. The engine speed can also be determined indirectly from the position of the trigger 120. Handheld power tools, such as tool 100, are associated with an idle operating mode in which no work is performed and an active operating mode in which the trigger is pressed and the engine speed increases compared to the idle operating mode. Engines typically have a maximum operating speed that can be achieved when the throttle is fully open (WOT).

[0035] The crankcase scavenging two-stroke engine 200 includes a cylinder wall 260 that partially defines the internal volume of a cylinder 220 through which a piston 210 reciprocates. This cylinder wall has at least an intake port 250 and an exhaust port 251, and may also have other ports such as a transfer port 252 and / or one or more airhead ports for stratified scavenging of the combustion engine 200. A transfer passage 253 extends between the crankcase 240 and the combustion chamber in the cylinder 220. The transfer passage has a transfer port 252 that opens into the cylinder 220.

[0036] The intake port 250 is used to supply air into the engine to enable combustion in the combustion chamber. Although fuel injection systems that inject fuel directly into the crankcase 240 or cylinder 220 are also known, the intake airflow through the intake port often also contains fuel in the air / fuel mixture. The exhaust port 251 is used to release exhaust from combustion out of the cylinder after combustion has occurred. The scavenging system of a two-stroke engine can be quite complex, having features such as stratified scavenging, in which clean air enters the cylinder through an airhead passage before the air / fuel mixture enters the cylinder. Stratigraphic scavenging can be achieved by complex passages formed in the piston skirt or by forming separate ports in the cylinder wall. This disclosure is applicable to a wide range of crankcase-scavenged two-stroke engines 200, with or without stratified scavenging. This disclosure is applicable to both carburetor-based engines and engines with fuel injection systems.

[0037] The combustion engine 200 is equipped with a lubrication system that reduces friction between different surfaces of the engine. Some two-stroke combustion engines are driven by fuel to which motor oil has been added, while others have a separate oil system configured to distribute a controlled amount of oil to the combustion engine during operation. It is important that the engine is not operated without lubrication, i.e., without a sufficient amount of oil in the engine during operation. Lubrication deficiency can occur for a variety of reasons, including failure of the oil distribution system. A common reason for lubrication deficiency in crankcase scavenging two-stroke engines is that the operator is using fuel that does not contain the appropriate amount of motor oil additive, i.e., the operator is using the wrong type of fuel.

[0038] Engine 200 is associated with an idle operating mode and an active operating mode. The idle operating mode is a standby operating mode obtained when the engine is started without trigger 120 being pressed. The active operating mode is obtained by activating the tool, such as by opening the engine throttle and pressing trigger 120 to accelerate the engine. The speed ω of engine 200 is higher in the active operating mode compared to the idle operating mode.

[0039] The engine 200 includes at least one engine vibration sensor 270, which is positioned and connected to the cylinder wall 260, to sense vibrations from the engine 200 and output an engine vibration signal 275. The engine also includes, or is at least associated with, a control unit 280 configured to detect lubrication deficiencies in the engine based on engine vibration signals in at least one delimited frequency band. This means that the control unit monitors engine vibrations frequency-selectively. The control unit may, for example, monitor vibrations in a high-frequency band above a certain start frequency and / or a low-frequency band below a certain end frequency. The control unit may also process vibration signals in one or more different frequency bands delimited by their respective start and end frequencies. A delimited frequency band is generally a subset of frequencies that the control unit processes in some way.

[0040] The control unit 280 can perform frequency-selective processing of the engine vibration signal 275 by applying analog or digital frequency filters such as low-pass filters, high-pass filters, or band-pass filters. Alternatively, the control unit 280 may perform frequency-selective processing of the engine vibration signal 275 by signal processing operations such as Fourier transforming the engine vibration signal. Generally, the control unit 280 applies different detection rules to detect lubrication deficiencies depending on a specific frequency band being monitored.

[0041] The engine 200 also includes a control unit 280 configured to detect lubrication deficiencies within the engine 200, preferably based on an engine vibration signal 275 and the operating mode of the engine 200. In other words, lubrication deficiency detection is based on both engine vibration and engine speed. Through practical experiments, it has been found that combining frequency-selective processing of the engine vibration signal with engine speed adjustment is particularly advantageous. Specifically, lubrication deficiency detection is performed frequency-selectively by attempting to detect lubrication deficiency only when the engine is operating above idle speed, monitoring different frequency bands of the engine vibration signal, and applying different lubrication deficiency detection principles to different frequency bands of the engine vibration signal.

[0042] A lookup table (LUT), analytical functions, etc., can be used to roughly convert between the trigger position or throttle state and the engine speed and / or operating mode of the engine 200. Therefore, the data indicating the trigger position and / or throttle state is considered equivalent to the engine speed data here and indicates the engine's operating state. Accordingly, according to some embodiments, the control unit 280 is configured to detect lubrication deficiency in the engine 200 based on the engine vibration signal 275 and also based on the throttle state and / or trigger position.

[0043] Using LUTs, analysis functions, etc., it is also possible to roughly convert the amplitude of engine vibration to the engine speed and / or operating mode of engine 200. Therefore, the data showing the amplitude of vibration is considered equivalent to the engine speed data here and indicates the operating state of the engine. Accordingly, according to some embodiments, the control unit 280 is configured to detect insufficient lubrication in engine 200 based on the engine vibration signal 275, provided that the amplitude of engine vibration is sufficiently strong (e.g., exceeds a threshold). It is also possible to weight the engine vibration data by its amplitude so that strong engine vibrations (during active operating mode) are given more consideration than weak engine vibrations (during idling, etc.) when detecting insufficient engine lubrication.

[0044] The engine vibration sensor 270 is connected to the control unit 280 via an interface wire that transmits the engine vibration signal 275. The interface between the engine vibration sensor 270 and the control unit 280 can be single-ended or differential (one or two wires).

[0045] The control unit 280 can implement a lubrication deficiency detection function that activates as soon as the engine leaves idle mode and is otherwise deactivated. When in active mode, the control unit monitors vibrations generated by the combustion engine and looks for signs of lubrication deficiency. It is understood that the detection efficiency of lubrication deficiency detection by the control unit is improved when the detection routine focuses on the period during which the combustion engine is operating at an engine speed above idle speed. This is because vibration patterns indicating lubrication deficiency become more pronounced at higher engine speeds. Two-stroke combustion engines can also operate at idle speed for extended periods despite typically suffering from lubrication deficiency. Therefore, detecting lubrication deficiency is less critical when the engine is in idle mode compared to when the two-stroke engine is in active mode.

[0046] An active operating mode can be defined as an engine operating mode in which the engine is operating at a speed exceeding a certain percentage of its maximum engine speed, such as a speed exceeding 80% of its maximum engine speed.

[0047] Detection may be conditional on the engine operating in active mode. In this case, if the engine is not in active mode, the detection routine is simply interrupted.

[0048] Detection can also be performed on weighted engine vibration signal data collected during engine operation, in which case the weights are configured as an increasing function of engine speed. In this way, engine vibration data collected during high-speed engine operation is given a greater weight compared to engine vibration data collected during low-speed engine operation, such as during idling. For example, suppose the control unit 280 collects an engine vibration data sample v[t], where t is the time index. The test variable can then be formed by weighting the data sample by engine speed ω, as follows:

[0049]

number

[0050] The weighting can be nonlinear, for example.

[0051]

number

[0052] The weights may be binary so as to consider only vibration data samples v[t] collected by the control unit 280 during engine operation above a certain engine speed threshold. Then, engine vibration data samples v[t] collected during engine operation below the engine speed threshold are discarded by the control unit 280.

[0053] The detection mechanism can be based on a simple thresholding of the amplitude of the oscillation or on other test statistics after some low-pass filtering or averaging, and of course other more advanced detection principles can also be applied here. The test statistic T[t] can be formed, for example, over time t as follows:

[0054]

number

[0055] Here, w ≪ 1 is the filter weight, and f(v'[t]) is either the absolute value f(v'[t]) = |v'[t]| or the squaring operation f(v'[t]) = (v'[t]). 2 These are examples of the MAGNITUDE function.

[0056] It should be understood that there are several different ways in which the control unit 280 can be configured to detect lubrication deficiency in the engine 200 based on the engine vibration signal 275 and the engine speed ω. One example is a simple threshold calculation applied to the test statistic T[t]. Several detection methods are known in the art. Therefore, detection methods will not be discussed in more detail herein.

[0057] It is known that at least two types of vibrations occur in two-stroke combustion engines. The first type of vibration occurs when the moving parts of the engine interact with each other during engine operation. For example, the piston 210 does not slide perfectly evenly against the cylinder wall, even when there is a sufficiently thick oil film between the piston and the cylinder wall. The relative motion between the crankshaft and the connecting rod, and the relative motion between the piston and the connecting rod, are also not perfectly uniform, but they generate vibrations during engine operation. This uneven movement between engine parts causes high-frequency vibrations, i.e., vibrations in the frequency band above approximately 50-100 kHz. Insufficient lubrication in the engine makes these vibrations more pronounced and increases the amplitude of high-frequency vibrations.

[0058] The second type of vibration occurs when the piston 210, particularly when one or more piston rings positioned on the piston, interact with ports 250, 251, and 252 in the cylinder wall. Figure 3A schematically shows an example of a piston ring 310 moving across port 320. As the piston ring crosses the port, it expands slightly into port 320 and collides with the port edge on its way through the port. This "collision" 330 generates an impact within the piston ring and the surrounding material that causes vibrations within the material, and the amplitude of the vibration A is schematically plotted against time t, as schematically shown here in Figure 3B. This generates vibrations in a lower frequency range compared to vibrations in a higher frequency range that result from the interaction of each part of the engine during use, causing uneven sliding motion. Interestingly, the amplitude of these low-frequency vibrations has been found to decrease during lubrication deficiencies, at least in crankcase scavenging two-stroke engines, as the vibrations are more strongly dampened by increased friction between the moving parts of the engine. In Figure 3B, this is shown by solid line 340 and dashed line 350, where dashed line 350 indicates the stronger damping observed during lubrication deficiency in the combustion engine 200.

[0059] Important vibration data is generated when the piston passes through one or more ports 320 in the cylinder wall. Therefore, when detecting lubrication deficiency, it makes sense to highlight the vibration data collected when the piston moves across the ports. Accordingly, according to some embodiments, the control unit 280 is configured to acquire crankshaft angle data indicating the crankshaft angle and to selectively acquire and / or process the engine vibration signal 275 as a function of the crankshaft angle. According to one example, the control unit 280 uses only the vibration data associated with a particular range of crankshaft angle. According to another example, the control unit 280 highlights the vibration data associated with a range of crankshaft angle, for example, by giving this data a greater weight in the detection process.

[0060] Figures 4A and 4B show the measurement results when an exemplary crankcase scavenging two-stroke engine operates alternately in idle mode 410 and active mode 420, i.e., when the trigger 120 of a handheld power tool is pressed first, then released, then pressed again, etc.

[0061] Figure 4A shows an example of the root mean square (RMS) values ​​of vibration amplitudes in the high-frequency range of approximately 100 kHz to 450 kHz in an oil-deficient operating scenario.400 Note that the amplitude of high-frequency vibrations shows an increasing trend over time.430 Lubrication deficiency can be detected, for example, by comparing the amplitude or power of vibrations in the high-frequency range to a threshold based on the perceived vibrations,440 or by using some other appropriate detection criterion.

[0062] Figure 4B shows an example of the root mean square (RMS) value of the amplitude of vibrations in the low frequency range of approximately 10 Hz to approximately 15 kHz in an oil-deficient operating scenario.450 In this case, the trend460 is rather decreasing, which supports the above argument.A threshold470 or any other suitable detection criterion can be used here as well to detect lubrication deficiency in the crankcase scavenging two-stroke engine200.

[0063] Based on this understanding of vibrations occurring within a crankcase-scavenging two-stroke engine, the control unit 280 can be configured to detect lubrication deficiencies in the engine 200 based on a decrease in vibration amplitude in a first frequency band below 20 kHz, preferably below 15 kHz, i.e., a low-frequency band. The first frequency band may be delimited to a lower end of about 5-10 Hz to avoid frequencies that are too low, which tend to appear as biases over shorter time periods. The vibration amplitude can be measured, for example, as the root mean square of vibrations picked up by the vibration sensor 270, or by some other suitable criterion for measuring vibration amplitude as described above.

[0064] The control unit 280 may also be configured to detect lubrication deficiencies in the engine 200 based on an increase in the amplitude of engine vibrations in a second frequency band above 50 kHz, preferably above 100 kHz, i.e., a high-frequency band. The second frequency band may be capped at around 450-500 kHz to avoid unnecessarily high requirements for the sampling frequency by the vibration sensor.

[0065] The detection criteria used by the control unit 280 to detect insufficient lubrication in the engine 200 can be based on simple thresholds 440, 470, as illustrated in Figures 4A and 4B. This is a computationally intensive detection mechanism and is therefore advantageous for the control unit 280, which has limited processing resources. However, more advanced detection mechanisms, such as statistical detection tests, are also conceivable. Detection may be based solely on monitored vibrations in a first frequency band (low frequency band), or on a combination of monitored vibrations in the first and second frequency bands.

[0066] According to some embodiments, lubrication deficiency can be declared when one of two detection criteria is met (at least one of the vibrations in the high-frequency band and the low-frequency band indicates lubrication deficiency).

[0067] According to several other embodiments, the detection of insufficient lubrication can only be declared if both of the two detection criteria are met simultaneously.

[0068] In some embodiments, the control unit 280 is configured to detect lubrication deficiencies in the engine 200 based on a machine learning function. The machine learning function, also called an artificial intelligence structure or function, is a mathematical model that is initially trained using exemplary vibration data from engines suffering from varying degrees of lubrication deficiencies and vibration data from a well-lubricated engine. Different datasets are also preferably collected from different use cases and may be collected only from specific types of tools, such as electric cutting machines when the control unit is used with the engine of an electric cutting machine, or from chainsaws when the control unit is used with the engine of a chainsaw. The machine learning function may include, for example, a random forest structure, a convolutional network, or some other machine learning structure and is trained using known techniques from machine learning. After convergence, i.e., after the machine learning structure has been trained to meet some predetermined detection performance criteria, such as a given percentage of false alarms and a given percentage of detection failures, it can be deployed within the control unit and used to detect lubrication deficiencies in the engine. Inputs to the machine learning function are engine vibration signals 275 and signals indicating engine operating modes, such as engine speed or trigger position.

[0069] In response to the detection of insufficient lubrication in engine 200, several actions can be taken. For example, the control unit 280 can be configured to limit the maximum engine speed or prevent engine operation in response to the detection of insufficient lubrication. This has the advantage of preventing insufficient lubrication from causing irreparable damage to engine 200.

[0070] The control unit 280 can also be configured to control the variable oil distribution system in response to the detection of insufficient lubrication. This reduces the overall amount of oil available, so that oil only needs to be added to the engine when actually needed. Alternatively, oil may be supplied using a timer function or the like, and if insufficient lubrication is detected, excess oil may be supplied. The oil distribution system can also be configured to distribute oil only when insufficient lubrication is detected by the control unit 280.

[0071] In some embodiments, the variable oil distribution system includes a sealed oil reservoir, i.e., an oil reservoir without a refill opening that is easily accessible to the operator. The sealed oil reservoir may be a plastic container without an opening, either directly attached to the oil pump or attached to the oil pump via an oil conduit. Handheld power tools are shipped with a sealed oil reservoir filled with oil, and the amount of oil in the reservoir is sized to last for the life of the tool.

[0072] The control unit 280 can be powered by some kind of energy collection mechanism, such as a Peltier element attached to the engine 200. This is advantageous because the mechanism does not require an external power source such as a battery or capacitor to operate.

[0073] At least one engine vibration sensor 270 preferably includes a piezoelectric element. Piezoelectricity is the property that a material generates an electric potential when subjected to mechanical stress such as bending, stretching, or compression. Materials exhibiting these properties are called piezoelectric materials, and there are many such materials. Subclasses of piezoelectric materials include, for example, piezoelectric ceramic materials, which include barium titanate, potassium niobate, sodium tungstate, and lead zirconate titanate (PZT). The latter is widely used in practical applications and is a mixture of lead zirconate and lead titanate. PZT has higher piezoelectric sensitivity and higher stability at high temperatures than many other materials. Furthermore, the piezoelectric properties of PZT can be formulated to be hard or soft. Vibration sensors based on piezoelectric elements have been shown to be cost-effective and reliable in detecting lubrication deficiencies in crankcase scavenging two-stroke engines of the type used in handheld power tools.

[0074] The engine vibration sensor 270 is advantageously positioned connected to ports 250, 251, and 252 of the cylinder wall 260. In this way, vibrations caused by the interaction between the piston rings and the ports are better captured by the vibration sensor. The amplitude of vibrations generated by the interaction between the piston and various elements of the cylinder wall naturally decreases with distance from the source, and therefore it is advantageous to capture the vibration as close to the source as possible. The engine 200 may be equipped with an engine vibration sensor 270 positioned connected to the scavenging passage of the engine 200. It is also advantageous to position several vibration sensors connected to the cylinder wall of the engine, so that each sensor covers a specific part of the cylinder wall, such as a port on a particular cylinder wall. Thus, the engine 200 selectively includes multiple engine vibration sensors positioned at various locations connected to the cylinder wall 260 to sense each vibration caused by the engine 200.

[0075] It is understood that strong vibrations from external sources, such as those generated by the interaction between the power tool and the workpiece, can adversely affect the control unit's ability to detect lubrication deficiencies in the engine based on vibrations occurring during engine operation. To mitigate the effects of vibrations from external sources, an additional vibration sensor can be positioned separately from the engine and used to sense such external vibrations. This data indicating the external vibrations can then be used to suppress interference generated by the external vibrations. In other words, the control unit 280 may be configured to receive data indicating external vibrations generated by an external source, and the control unit 280 is configured to detect lubrication deficiencies in the engine 200 based on a combination of the sensed engine vibrations and external vibrations.

[0076] Figure 5 shows an example of a signal processing structure for suppressing external vibrations. One or more vibration sensors are used to sense external vibrations 510 from the combustion engine or at one or more locations physically separated from at least the cylinder walls of the combustion engine. This data z is input to an equalizer structure 520, such as an adaptive finite impulse response (FIR) filter, which has a number of equalizer taps in a known manner. The output from this equalizer structure 520 is removed from the vibration sensor data captured by the vibration sensor 270 (530) before being supplied to the detector function in the control unit 280. A time delay by a delay element 540 is necessary to compensate for the delay suffered by the equalizer structure 520. The equalizer structure 520 can be adaptively updated, for example, based on the orthogonality principle, to orthogonalize or uncorrelated the difference signal e with the external vibration data z. For example, we can employ the least mean squares (LMS) update principle, where the l-th equalizer tap is updated in discrete-time instant m+1 as follows:

[0077]

number

[0078] Here, μ is a step size that can be determined adaptively by a fixed or known method. The adaptive equalizer structure 520 determines the correlation between the external vibration data z and the engine vibration data v and removes this correlation. This effectively removes interference from the external vibration data in the engine vibration data. This type of adaptive equalizer structure is generally known, so it will not be described in further detail here.

[0079] The techniques disclosed herein can also be described in relation to a method performed by a control unit 280 configured to be connected to a crankcase scavenging two-stroke engine 200, as shown in the flowchart of Figure 6. This method includes the steps of obtaining engine vibration data from a vibration sensor 270 connected to and positioned on the cylinder wall 260 when the engine 200 is in an active operating mode, and detecting a lubrication deficiency in the engine 200 based on the engine vibration data, Sa2.

[0080] According to some embodiments, the method also includes step Sa21 of suppressing vibrations from an external source in the engine vibration data based on data indicating vibrations from an external source.

[0081] Figure 7 shows an exemplary engine vibration sensor 270 attached to a control unit 280 via an interface wire that transmits an engine vibration signal 275 from the sensor 270 to the control unit 280. This engine vibration sensor 270 is manufactured in a way that allows for cost-effective large-scale production. Figure 8 is a flowchart illustrating this method. Figure 8 shows a method for manufacturing an engine vibration sensor 270, as described above and, for example, the sensor shown in Figure 2. This method includes step Sb1 of providing an engine vibration sensor body 710. This engine vibration sensor body can be formed as a cylindrical hollow component having a cup, i.e., a flat bottom and an internal volume large enough to receive a piezoelectric element such as a piezoelectric ceramic element. The sensor body may be formed of a metal such as brass, bronze, or other material that can be used in a soldering process. Metal-coated polymers and the like can also be used as the engine vibration sensor body. This method includes step B2 of placing a piezoelectric element 720 on the vibration sensor body 710 and adding solder paste 715 between the piezoelectric element 720 and the vibration sensor body 710. Any suitable solder paste can be used between the piezoelectric element 720 and the vibration sensor body 710, such as the type of solder paste used in reflow ovens for manufacturing printed circuit boards (PCBs). This method also includes step Sb3 of placing a counterweight element 730 on the piezoelectric element 720, in which case solder paste 725 is also applied between the piezoelectric element 720 and the counterweight element 730. The counterweight element 730 has dimensions and weight suitable for the engine 110, which can be determined in a direct manner from actual laboratory experiments and / or computer simulations. Thus, the counterweight element is designed to provide a strong and clear vibration signal output by the piezoelectric element in a desired frequency range, namely, a frequency range including the high frequencies described in relation to Figure 4A and the low frequencies described in relation to Figure 4B above. The counterweight element can also be formed from brass, bronze, or other solder-friendly material.Metal-coated polymers can also be used here, but the weight of the polymer may result in a considerably larger counterweight. Next, the entire assembly of the engine vibration sensor 270 is heated (step S4) to fix the parts together. Large quantities of engine vibration sensors can be manufactured in this manner, for example, using a pick-and-place machine and a reflow oven, similar to manufacturing methods for producing large quantities of PCBs. This method may also include step Sb5 of attaching interface wires to the engine vibration sensor body 710 and the counterweight element 730, although this step can also be performed when assembling the engine vibration sensor with the engine to be monitored for lubrication deficiencies. The interface wires can be attached by soldering or by any other mounting mechanism such as screw fasteners, interlocking fits, or friction-based connectors.

[0082] The space remaining between the piezoelectric element 720, the counterweight element 730, and the vibration sensor body 710 is filled with a suitable filler material 740 such as epoxy resin.

[0083] Figures 9A and 9B show an exemplary crankcase scavenging two-stroke engine 900 suitable for a handheld power tool of the type shown in Figure 1. Engine 900 can also be used in other types of tools and machines such as floor saws. Engine 900 is an exemplary engine, and it should be understood that the technology disclosed herein is generally applicable to several different types of two-stroke combustion engines.

[0084] The engine 900 is equipped with a spark plug 910 configured to ignite the fuel-air mixture in the engine cylinder. The spark is generated from an electrical pulse transmitted from the engine's ignition module 920 in a known manner. The electrical connection 925 between the ignition module 920 and the spark plug 910 is schematically shown by a dashed line in Figure 9A.

[0085] The engine further includes a flywheel 930 that provides a cooling airflow to remove heat from the engine 900. This flywheel is also used by an ignition module 920 to collect energy by a magnet and coil configuration. The ignition module is generally a component enclosed in a housing that is fixedly mounted to the engine's motor block 940. The ignition module typically includes a coil configured to receive electrical energy from magnets attached in known ways to the engine's flywheel or other rotating parts. The energy obtained through the coil is transmitted in pulses to a spark plug 910, each pulse generating a spark by the spark plug. The ignition module typically includes a circuit configured to control the timing of the ignition pulses transmitted to the spark plug 910.

[0086] At least one vibration sensor 270 is optionally integrated with the ignition module 920, i.e., contained within the same housing as the coil and control circuit for the electrical pulses transmitted from the ignition module 920 to the spark plug 910. An example in Figure 9A shows two vibration sensors integrated with the ignition module. A control unit configured to detect lubrication deficiencies based on vibration signals from the vibration sensors 270 may also be incorporated within the ignition module 920. The vibration sensors 270 integrated with the ignition module are fixed to the engine's motor block 940 by similar fastening means as the ignition module 920. Vibrations from the engine propagate to the ignition module and reach the vibration sensors 270.

[0087] In some embodiments, the ignition module 920 is configured to control the ignition of the engine 900 based on the detection of insufficient lubrication by the control unit 280. The control circuit within the ignition module can, for example, refrain from transmitting some electrical pulses, i.e., cut off some ignitions, thereby reducing the engine speed.

[0088] The feature of integrating the engine vibration sensor with the ignition module is closely related to any of the other technical features described herein. Referring also to Figure 2, a crankcase scavenging two-stroke engine 200, 900 is disclosed, comprising a cylinder wall 260 having an intake port 250 and an exhaust port 251, a spark plug 910, and an ignition module 920 electrically connected to the spark plug 910. The engine 200, 900 includes at least one engine vibration sensor 270, which is configured to sense vibrations from the engine 200, 900 and output an engine vibration signal 275. The engine 200, 900 also includes a control unit 280, which is configured to detect lubrication deficiencies in the engine 200, 900 based on the engine vibration signal 275. The engine vibration sensor is integrated with the ignition module 920 of the crankcase scavenging two-stroke engine 200, 900.

[0089] The engine 900 further comprises a scavenging passage 950 (also known as a transfer passage) and a pressure reducing valve 960. One or more engine vibration sensors 270 may be positioned connected to the scavenging passage 950 of the engine 900 and / or connected to the pressure reducing valve 960.

[0090] The scavenging passage 950 can be at least partially demarcated by a scavenging passage cover, as shown in the example in Figures 9A and 9B. In this case, at least one engine vibration sensor 270 can be mounted on the outer surface of the scavenging passage cover. This simplifies the assembly of the engine 900.

[0091] The pressure reducing valve 960 is generally a manually operated valve configured to release pressure in the combustion chambers of engines 200, 900 during the starting procedure. At least one engine vibration sensor 270 may be advantageously mounted to engines 200, 900 and connected to the pressure reducing valve 960, as schematically shown in Figure 9B.

[0092] The control unit 280 is configured to acquire crankshaft angle data indicating the crankshaft angle. In this case, the control unit 280 can be configured to selectively acquire the engine vibration signal 275 as a function of the crankshaft angle. In this way, the acquisition of vibration data from the vibration sensor 270 can be focused on the point in time when the piston passes a point of interest beyond the cylinder, such as ports 250 and 251 on the cylinder wall. The crankshaft angle from which vibration data should be acquired may be pre-set in a LUT or the like. The crankshaft angle data can also be used in a weighting scheme to highlight portions of vibration data associated with a specific crankshaft angle range, such as the angle range corresponding to passing over ports 250 and 251 on the cylinder wall.

[0093] In some embodiments, a plane that coincides with and intersects the central axis of the cylinders of the engine 900 divides the engine into a low-temperature half and a high-temperature half. The high-temperature half is the side of the engine where the exhaust is located, i.e., the high-temperature half of the engine includes the exhaust ports of the cylinders. At least one engine vibration sensor 270 is mounted on the low-temperature half of the engine, which is less affected by the heat from the engine.

[0094] The specific vibrations generated by engines experiencing insufficient lubrication are relatively weak and can be difficult to detect reliably. Therefore, it is advantageous to amplify the vibration signal from the vibration sensor near the vibration sensor itself. Figure 10 schematically shows a vibration sensor design in which a vibration signal amplifier is positioned close to the vibration sensor to amplify the vibration signal output from the vibration sensor. In this design, the engine vibration sensor 270 includes a piezoelectric element 1010 mounted on a printed circuit board (PCB) 1020. The PCB houses a vibration signal amplifier 1030 configured to amplify the output signal from the piezoelectric element 1010. In the example shown in Figure 10, the piezoelectric element 1010 and the amplifier 1030 are mounted on opposite sides of the PCB 1020 and connected by a signal conduit that penetrates the PCB.

[0095] PCB1020 also optionally includes processing circuits 1040 and 1050 electrically connected to the vibration signal amplifier 1030, such as the control unit 280. The signal processing circuits may include field-programmable devices.

[0096] Furthermore, the various control units 280 described herein can be configured to detect any of the following based on the engine vibration signal 275: a faulty air filter, a malfunctioning engine bearing, and a damaged crankshaft. Detection can be carried out by known signal processing techniques, including machine learning in which the detection algorithm is trained using vibration data obtained from engines with various faults. Computer simulations can also be used to train the machine learning algorithms.

[0097] Figure 11 shows an example of a three-dimensional (3D) vibration sensor. This sensor is configured to measure vibrations along three orthogonal axes, indicated as x, y, and z in Figure 11. In the example in Figure 11, the three piezoelectric elements 1100, 1110, and 1120 are positioned so that their different axes x, y, and z are perpendicular to the plane of the piezoelectric sensor. Vibration data collected in this way has more subtle nuances compared to one-dimensional vibration data. Obtaining vibration data in multiple dimensions can be advantageous, especially when machine learning detection techniques are used.

[0098] Figure 12 schematically shows the general components of the control unit 280 with respect to numerous functional units. The processing circuit 1210 is provided using one or more suitable central processing units, CPUs, multiprocessors, microcontrollers, digital signal processors, etc., in any combination, capable of executing software instructions stored in a computer program product in the form of a storage medium 1230, for example. The processing circuit 1210 may further be provided as at least one application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA).

[0099] Specifically, the processing circuit 1210 is configured to cause the control unit 280 to perform a set of operations or steps, such as the method described herein. For example, the storage medium 1230 may store a set of operations, and the processing circuit 1210 may be configured to read a set of operations from the storage medium 1230 in order to cause the device to perform the set of operations. The set of operations can be provided as a set of executable instructions. Accordingly, the processing circuit 1210 is configured to perform the method disclosed herein.

[0100] Furthermore, the storage medium 1230 may include a persistent storage device which is, for example, one or a combination of magnetic memory, optical memory, solid-state memory, or remotely mounted memory.

[0101] The control unit 280 may further include an interface 1220 for communicating with at least one external device, such as a vibration sensor 270 or a plurality of vibration sensors 270. Accordingly, the interface 1220 may include one or more transmitters and receivers, including analog and digital components and an appropriate number of ports for wired or wireless communication.

[0102] The processing circuit 1210 controls the general operation of the control unit 280 by, for example, transmitting data and control signals to the interface 1220 and the storage medium 1230, receiving data and reports from the interface 1220, and retrieving data and commands from the storage medium 1230.

[0103] The control unit 280 may include a frequency processing unit 1215 configured to perform frequency selective processing of the engine vibration signal 275 from the vibration sensor 270. Frequency selective processing may include, for example, digital or analog filtering to isolate specific frequency bands from the engine vibration signal.

[0104] Also disclosed herein is a computer-readable medium that carries a computer program, including program code means for performing the methods described herein, when the program product is executed on a computer. The computer-readable medium and the code means together can form a computer program product.

Claims

1. A crankcase scavenging two-stroke engine (200, 900) having a cylinder wall (260) with an intake port (250) and an exhaust port (251), The engine (200, 900) is associated with an idle operating mode and an active operating mode, and the speed (ω) of the engine (200, 900) is faster in the active operating mode compared to the idle operating mode. The engine (200, 900) includes at least one engine vibration sensor (270) configured to sense vibrations caused by the engine (200, 900) and output an engine vibration signal (275), A control unit (280) configured to detect insufficient lubrication in the engine (200, 900) based on the engine vibration signal (275), Engines equipped with (200, 900).

2. The engine (200, 900) according to claim 1, wherein the detection of insufficient lubrication by the control unit (280) is conditional on the engine (200, 900) being in operation in the active operating mode.

3. The engine (200, 900) according to claim 1 or 2, wherein the at least one engine vibration sensor (270) includes a piezoelectric element.

4. The control unit (280) is configured to detect insufficient lubrication in the engine (200, 900) based on the engine vibration signal (275) in at least one segmented frequency band, wherein the at least one frequency band includes a first frequency band less than 20 kHz, preferably less than 15 kHz, and the control unit (280) is configured to detect insufficient lubrication in the engine (200, 900) based on a decrease in the amplitude of vibration in the first frequency band, according to any one of claims 1 to 3.

5. The engine (200, 900) according to claim 4, wherein the first frequency band includes frequencies exceeding 5 Hz, preferably exceeding 10 Hz.

6. The engine (200, 900) according to any one of claims 1 to 5, wherein the control unit (280) is configured to detect insufficient lubrication of the engine (200, 900) based on the engine vibration signal (275) in at least one separated frequency band, the at least one frequency band includes a second frequency band exceeding 50 kHz, preferably exceeding 100 kHz, and the control unit (280) is configured to detect insufficient lubrication of the engine (200, 900) based on an increase in the amplitude of engine vibration in the second frequency band.

7. The engine (200, 900) according to claim 6, wherein the second frequency band includes frequencies less than 500 kHz, preferably less than 450 kHz.

8. The engine (200, 900) according to any one of claims 1 to 7, wherein at least one engine vibration sensor (270) is connected to and positioned in a port (250, 251, 252) of the cylinder wall (260).

9. The engine (200, 900) according to any one of claims 1 to 8, wherein at least one engine vibration sensor (270) is located in connection with the scavenging passage (950) of the engine (200, 900).

10. The engine (200, 900) according to any one of claims 1 to 9, wherein the scavenging passage (950) is at least partially separated by a scavenging passage cover, and at least one engine vibration sensor (270) is mounted on the outer surface of the scavenging passage cover.

11. An engine (200, 900) according to any one of claims 1 to 10, comprising a spark plug (910) and an ignition module (920) electrically connected to the spark plug (910) and fixedly mounted to the motor block (940) of the engine (200, 900), wherein at least one engine vibration sensor (270) is integrated with the ignition module (920).

12. The engine (200, 900) according to claim 11, wherein the ignition module (920) is configured to control the ignition of the engine (200, 900) to reduce the engine speed in response to the detection of insufficient lubrication by the control unit (280).

13. An engine (200, 900) according to any one of claims 1 to 12, comprising a pressure reducing valve (960) configured to release pressure in the combustion chamber of the engine (200, 900) during a starting procedure, and at least one engine vibration sensor (270) connected to the pressure reducing valve (960) and mounted on the engine (200, 900).

14. The engine (200, 900) according to any one of claims 1 to 13, wherein at least one engine vibration sensor (270) is connected to and positioned on the cylinder wall (260).

15. An engine (200, 900) according to any one of claims 1 to 14, wherein a plane that coincides with and intersects the central axis of the cylinders of the engine (200, 900) divides the engine into a low-temperature half and a high-temperature half, the high-temperature half of the engine includes the exhaust port of the cylinder, and at least one engine vibration sensor (270) is mounted on the low-temperature half of the engine (200, 900).

16. The engine (200, 900) according to any one of claims 1 to 15, wherein the control unit (280) is configured to acquire crankshaft angle data indicating the crankshaft angle of the engine (200, 900), and the control unit (280) is configured to selectively acquire and / or process the engine vibration signal (275) as a function of the crankshaft angle.

17. The engine (200, 900) according to any one of claims 1 to 16, wherein the control unit (280) is configured to limit the maximum engine speed or prevent engine operation in response to detection of insufficient lubrication.

18. A handheld power tool comprising an engine (200, 900) according to any one of claims 1 to 17.

19. A method performed by a control unit (280) positioned in connection with a crankcase scavenging two-stroke engine (200, 900) having a cylinder wall (260) having an intake port (250) and an exhaust port (251), The engine (200, 900) is associated with an idle operating mode and an active operating mode, and the speed (ω) of the engine (200, 900) is faster in the active operating mode compared to the idle operating mode. The aforementioned method, Step (Sa1) of acquiring engine vibration data from a vibration sensor (270) that is connected to the cylinder wall (260) or integrated into the ignition module (920), The steps include detecting insufficient lubrication of the engine (200, 900) based on the engine vibration data (Sa2), A method that includes this.

20. A crankcase scavenging two-stroke engine (200, 900) having a cylinder wall (260) with an intake port (250) and an exhaust port (251), The engine (200, 900) includes at least one engine vibration sensor (270) connected to and positioned on the cylinder wall (260) to sense vibrations caused by the engine (200, 900), A control unit (280) configured to detect insufficient lubrication of the engine (200, 900) based on detected engine vibrations, It is equipped with, The engine vibration sensor (270) includes a piezoelectric element and is located in the engine (200, 900).

21. A crankcase scavenging two-stroke engine (200, 900) having a cylinder wall (260) with an intake port (250) and an exhaust port (251), The engine (200, 900) comprises a control unit (280) and at least one engine vibration sensor (270) connected to the cylinder wall (260) and sensing vibrations caused by the engine (200, 900). The control unit (280) is configured to detect insufficient lubrication of the engine (200, 900) based on a decrease in the amplitude of vibration in a first frequency band of less than 20 kHz, preferably less than 15 kHz. Engine (200, 900).

22. A crankcase scavenging two-stroke engine (200, 900) having a cylinder wall (260) with an intake port (250) and an exhaust port (251), The engine (200, 900) comprises a control unit (280) and at least one engine vibration sensor (270) connected to the cylinder wall (260) and sensing vibrations caused by the engine (200, 900). The control unit (280) is configured to receive data indicating external vibrations generated by an external source. The control unit (280) is configured to detect insufficient lubrication of the engine (200, 900) based on a combination of data indicating the sensed engine vibration and external vibration. Engine (200, 900).

23. A method for manufacturing an engine vibration sensor (270), Step (Sb1) of installing the engine vibration sensor body (710), Step (Sb2) involves applying solder paste between the piezoelectric element (720) and the engine vibration sensor body (710) to place the piezoelectric element (720) on the engine vibration sensor body (710), Step (Sb3) of applying solder paste between the piezoelectric element (720) and the counterweight element (730) and placing the counterweight element (730) on the piezoelectric element (720), The steps include heating the engine vibration sensor (270) assembly (Sb4), A method that includes this.

24. Engine vibration sensor (270), Engine vibration sensor body (710) and A piezoelectric element (720) is soldered to the surface of the engine vibration sensor body (710), A counterweight element (730) is soldered to the piezoelectric element (720) on the opposite side from the engine vibration sensor body (710), An interface wire configured to transmit an engine vibration signal (275) to a control unit (280), An engine vibration sensor (270) equipped with this.

25. A crankcase scavenging two-stroke engine (200, 900) comprising a cylinder wall (260) having an intake port (250) and an exhaust port (251), a spark plug (910), and an ignition module (920) electrically connected to the spark plug (910), The engine (200, 900) includes an engine vibration sensor (270) configured to detect vibrations caused by the engine (200, 900) and output an engine vibration signal (275), A control unit (280) configured to detect insufficient lubrication of the engine (200, 900) based on the engine vibration signal (275), It is equipped with, The engine vibration sensor is either connected to the cylinder wall (260) or integrated with the ignition module (920) of the crankcase scavenging two-stroke engine (200, 900). Engine (200, 900).

26. A crankcase scavenging two-stroke engine (200, 900) having a cylinder wall (260) with an intake port (250) and an exhaust port (251), The engine (200, 900) includes at least one engine vibration sensor (270) configured to sense vibrations caused by the engine (200, 900) and output an engine vibration signal (275), A control unit (280) configured to detect insufficient lubrication of the engine (200, 900) based on the engine vibration signal (275), It is equipped with, The control unit (280) is configured to detect insufficient lubrication of the engine (200, 900) based on a decrease in the amplitude of vibration in a first frequency band and an increase in the amplitude of engine vibration in a second frequency band above the first frequency band. Engine (200, 900).

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