Technical field

The present disclosure relates to a lubrication monitoring system configured to monitor a supply of lubricant in a hand-held cutting tool having a cutting unit, a lubricant tank and a conduit configured to duct a flow of lubricant from the tank to the cutting unit, wherein the lubrication monitoring system comprises a heating element and a sensor arrangement, the heating element being configured to heat said flow.

Background

One example of such a monitoring system is disclosed in WO-2019/088891 -A1 . A lubrication system includes a tank and a conduit ducting lubricant from the tank to a cutting unit of the cutting tool. There is provided a heating element and a control unit, the heating element heating a portion of the lubrication system and the control unit monitoring the supply of lubricant detecting by changes in temperature of the portion of the lubrication system.

One general problem with systems of this kind is to improve the reliability of the monitoring of the supply of lubricant.

Summary

One object of the present disclosure is therefore to provide a lubrication monitoring system with improved reliability with regard to the monitoring of the supply of lubricant.

This object is achieved by means of a lubrication monitoring system as defined in claim 1 . More specifically, in a lubrication monitoring system of the initially mentioned kind, the sensor arrangement comprises a first sensor located in the flow, upstream of the heating element, and a second one downstream of the heating element. The lubrication monitoring system outputs a monitoring signal based on a sensed temperature difference between the first and the second sensor. This provides a reliable monitoring of the lubricant flow, which is affected by changes in ambient temperature, for instance, only to a small extent.

The arrangement may comprise a sensor container forming a lubricant flow channel from an input to an output and a circuit board fitted inside the sensor container and carrying said heating element and said first and second sensors, reaching into the flow channel. This connects the heating element and the sensors to the lubricant flow in an efficient manner. The sensor container may further comprise a connector channel, separate from the flow channel, where cables connecting to the circuit board run.

Typically, the sensor container may be sealed on top of the circuit board by means of a molded resin.

The first and second sensors may be NTC resistors.

The present disclosure further considers a lubrication monitoring system configured to monitor a supply of lubricant in a hand-held cutting tool having a cutting unit, a lubricant tank and a conduit configured to duct a flow of lubricant from the tank to the cutting unit, wherein the lubrication monitoring system comprises a sensor arrangement, and outputs a lubrication monitoring signal to a control unit depending on the lubricant flow. The monitoring system is configured to output a lubrication monitoring signal in the form of a periodically varying voltage upon detection of a lubricant flow exceeding a predetermined threshold. This provides a reliable transfer of lubricant flow information as the absence of the periodically varying voltage can easily be detected at the control unit.

The control unit may be configured to detect a constant low voltage if the lubricant flow is insufficient, and a constant high voltage if the monitoring system becomes disconnected. This allows the control unit to distinguish between those two fault conditions.

The present disclosure further considers a hand-held cutting tool having a cutting unit, a lubricant tank and a conduit configured to duct a flow of lubricant from the lubricant tank to the cutting unit, the handheld cutting tool further comprising a lubrication monitoring device configured to monitor the lubricant flow. The lubricant tank comprises an outer recess, wherein the lubrication monitoring unit is located in the recess. This offers the possibility of producing a complete lubrication unit, which may be efficiently incorporated in an assembling line.

Typically, the lubrication monitoring unit may be fitted in the recess with a snap fit to facilitate assembling. In any of the scenarios outlined above, the tool may typically be a battery-operated chainsaw.

Brief description of the drawings

Fig 1 shows a chain saw.

Fig 2A shows a first exploded view of an oil sensor unit.

Fig 2B shows a second exploded view of the oil sensor unit.

Fig 2C illustrates schematically features of the oil sensor and the feeding of oil to a saw chain.

Fig 3 shows the oil sensor attached to an oil tank.

Figs 4A-D illustrate the oil sensor communicating with a control unit of the chain saw.

Detailed description

The present disclosure relates to a lubrication monitoring system for a chainsaw, and to a chainsaw comprising such a system. An example of a chain saw 1 is illustrated in fig 1 . The chainsaw comprises a guide bar 3 on which a saw chain 5 runs, driven by a motor inside the chainsaw housing 6. The chainsaw is operated by a user holding the handles 7 thereof. In the illustrated case, the chainsaw is powered by a replaceable battery 8 secured in a battery compartment 10.

During operation, the saw chain 5 is lubricated by a steady but small flow of lubricant such as petroleum or vegetable oil, to ensure that the saw chain 5 runs smoothly on the guide bar 3 and that the individual saw chain links can pivot in relation to each other without significant friction. Oil is fed from a lubricant oil tank, the cap 13 of which is indicated in fig 1 . The lubricant flow may be achieved by means of a pump operating based on the chainsaw motor speed providing a flow that varies slightly based on speed.

While the present disclosure in principle is applicable to both electric chainsaws and chainsaws driven by an internal combustion engine, ICE, it is particularly advantageous in relation to electric chainsaws, whether battery-operated or connected to a power outlet means of a cable. In ICE driven chainsaws the oil tank may be dimensioned such that the lubricant tank is almost empty at the same time as the petrol tank is empty, meaning that the skilled user may learn to replenish the supply of both fluids at the same time. In battery-operated saws on the other hand, the battery 8 usually needs to be replaced and/or recharged sooner, and even sooner as the battery ages. In power outlet powered saws, the saw can in principle be operated indefinitely. In electric saws, therefore there is no trigger to replenish the lubricant supply, and it may therefore be useful to monitor the lubricant flow and warn the user before the saw chain 5 runs dry. However, also in ICE-operated chainsaws, it may be useful to monitor the lubricant flow as it may be blocked by contaminations, for instance.

The present disclosure therefore describes an improved lubrication monitoring system which can be used in this context. Fig 2A shows a first exploded view of a lubrication monitoring sensor unit 15. The sensor unit 15 comprises an inlet 17 to and an outlet 19 from a sensor container 21 . In the sensor container 21 , a circuit board 23 comprising an electric system is to be fitted. The sensor container 21 comprises a lubricant flow channel 25. When the circuit board 23 is fitted in the container 21 , a closed passage is formed by the lubricant flow channel 25 from the container inlet 17 to the outlet 19.

The sensor container 21 further comprises a connector channel 27, separate from the flow channel 25, where cables connecting to the circuit board 23 can run. The sensor container 21 can typically be produced by injection moulding a plastic material. The sensor container 21 can further be closed by a lid, which is not shown in fig 2A, or the remaining space on top of the circuit board 23 may be filled with a molded resin to seal the interior of the container 21 .

Fig 2B shows a second exploded view of the lubrication monitoring sensor unit 15, where the bottom side of the circuit board 23 is exposed. The circuit board 23 includes, on the bottom side, a heating element 29, which reaches into the lubricant flow channel 25 to heat the lubricant therein as is best seen in the enlarged portion of fig 2B. This heating element 29 may in itself be useful for instance in very cold weather, where the viscosity of the lubricant may otherwise become too high be provided properly to the saw chain. Typically, the heating element 29 is a power resistor capable of producing about 0.5 W when powered by direct current at about 9 V. The bottom side further comprises a first 31 and a second 33 temperature sensor, which also reach into the lubricant flow channel 25. In the lubrication flow, the first sensor 31 is located upstream of the heating element 29, and the second sensor 33 downstream of the heating element 29. Typically, the temperature sensors 31 , 33 may comprise NTC resistors, which may be identical. However, the skilled person is aware of several other types of temperature sensors that are conceivable in this context such PTC resistors, RTD resistors, thermocouples, etc.

Fig 2C illustrates schematically features of the lubrication monitoring sensing arrangement and the feeding of lubricant to a saw chain 5 on a guide bar 3. There is provided a lubricant tank 41 containing a lubricant 43 that may be replenished through an opening covered by the cap 13 mentioned earlier. A conduit 45 connects the lubricant tank with the guide bar 3 at a location close to the saw chain 5. This conduit may include a plurality of tubes as will be shown. A lubricant pump 47, for instance comprising an impeller, feeds an amount of oil to the saw chain 5. As mentioned, one part of the lubricant conduit is made up of the lubrication monitoring unit 15, and the heating element 29 as well as the first and second temperature sensors 31 , 33 reach into the lubricant flow.

As one sensor 31 is located upstream of the heating element 29 and the other 33 downstream thereof, the latter will sense a higher temperature if the there is a significant flow of lubricant through the conduit 45. The lubrication monitoring unit 15 may therefore output a monitoring signal which is based on a sensed temperature difference between the first and the second sensors 31 , 33. The monitoring unit 15 may communicate with a chainsaw control unit 49 in a manner to be shown and may communicate an OK signal as long as the lubricant flow is acceptable, or may communicate an estimated lubricant flow or the temperature difference itself, for instance.

As long as the lubricant tank 41 has a remaining amount of lubricant 43, the lubricant flow is not blocked and the lubricant pump 47 is working, there will be a significant temperature difference sensed in between the first and second sensors 41 , 43. If this difference falls under a predetermined threshold however, it may be assumed that the saw chain lubrication is not sufficient. If so, a control system 49 to which the lubrication monitoring unit 15 is connected may produce a fault indication and/or disable or limit the operation of the saw to prevent damaging or degrading the saw chain 5 or other components of the chainsaw 1 .

Compared to the initially mentioned known lubrication monitoring system where temperature changes are detected, this arrangement is influenced less by changes in ambient temperature, for instance, since changes in ambient temperature changes the temperature reading of both sensors alike and not the differential temperature. This provides an improved reliability.

Fig 3 shows the lubrication monitoring sensor unit 15 attached to an oil tank 41 . It has been found that it is advantageous to arrange the lubrication monitoring unit 15 together with the lubricant tank 41 as this simplifies production, maintenance, and repair of the chainsaw 1 . In the present disclosure it is proposed to provide an outer recess 51 in the lubricant tank 41 which can be occupied by the lubrication monitoring unit 15. The lubricant tank 41 may for instance be formed from two pieces, both produced in plastic by injection moulding where the outer recess 51 is formed in one of those as a part of the mould.

As shown in fig 3, the lubricant conduit 45 may be formed by a first tube 53 connecting the lubricant tank 41 with the input 17 of the lubrication monitoring unit 15, a second tube 55 connecting the output 19 of the lubrication monitoring unit 15 to the lubricant pump 47, and a third tube 57 connecting the lubricant pump 47 with a nozzle 59 adapted to rest against the guide bar 3 of the chainsaw 1 . Thus, as shown the lubricating system as a whole may be provided as an assembled unit.

Typically, there may be provided a form-fitting arrangement such that the lubrication monitoring unit 15 can be attached in the recess 51 of the lubricant tank 41 by being slid therein with a snap fit locking feature.

Fig 4A illustrates the lubrication monitoring sensor 15 unit communicating with a control unit 49 of the chainsaw. In fig 4B it is illustrated that the lubrication monitoring sensor 15 has measured an acceptable lubricant flow and thus communicates an OK signal. This is done by providing an output to the control unit 49 which varies between a high and a low state in terms of voltage forming a square wave, for instance, using a switching circuit. When the lubricant tank 41 is empty, the flow disappears and the temperature difference between the sensors 31 , 33 is no longer present due to the absence of a lubricant flow over the heating element 29. The lubrication monitoring sensor 15 then may output a constant low voltage, as illustrated in fig 4C, which is detected by the control unit 49 that may then for instance disable the chainsaw and provide a visual warning to the user, for instance using a user interface.

A third condition is illustrated in fig 4D where the lubrication monitoring sensor 15 has been disconnected or the cable in between the lubrication monitoring sensor 15 and the control unit 49 has become faulty. In that case for instance a pull-up resistor at the input of the control unit 49 may force the input to a constant high state which is detected as a fault indication by the control unit, which may for instance provide a visual warning using the user interface. Thanks to the above-described arrangement, the lubrication monitoring sensor 15 actively informs the control unit if the lubrication flow is sufficient and the latter is capable of detecting both insufficient flow and a faulty sensor connection with a very simple communications scheme. It would however be possible to apply other and more complicated communication protocols with the hardware shown in figs 1-3 such as CAN (Controller Area Network) bus protocols or a protocol varying the switching frequency depending on the flow for instance.

The invention is not restricted to the described embodiments and may be varied and altered in different ways within the scope of the appended claims.