SE544294C2

SE544294C2 - Lawnmower and lawnmower drive wheel

Info

Publication number: SE544294C2
Application number: SE2050451A
Authority: SE
Inventors: Lars Ederfors
Original assignee: Husqvarna Ab
Priority date: 2020-04-21
Filing date: 2020-04-21
Publication date: 2022-03-29
Also published as: WO2021215980A1; DE112021000267T5; SE2050451A1

Abstract

A lawnmower (1) is disclosed comprising at least one drive wheel (3) and a propulsion motor (4) configured to rotate the drive wheel (3). The drive wheel (3) comprises a first wheel member (5) connected to the propulsion motor (4), a second wheel member (7) comprising a ground engaging surface (7’) configured to abut against a ground surface (22) during operation of the lawnmower (1), and a number of grip enhancing members (8) movably arranged relative to the ground engaging surface (7’) between a retracted and an extracted position. The drive wheel (3) further comprises a mechanism (9) configured to move the grip enhancing members (8) between the retracted and the extracted position based on a torque between the first and second wheel members (5, 7). The present disclosure further relates to a drive wheel (3) for a lawnmower (1).

Description

Lawnmower and Lawnmower Drive Wheel TECHNICAL FIELDThe present disclosure relates to lawnmower comprising at least one drive wheel and apropulsion motor configured to rotate the drive wheel. The present disclosure further relates to a drive wheel for a lawnmower.

BACKGROUND Various types of lawnmowers exist on today's market. Examples are walk-behind mowers,riding mowers, and self-propelled robotic lawnmowers. A walk-behind mower is a lawnmowerusually comprising an elongated handle allowing a user to push, and/or to guide, thelawnmower. Some walk-behind mowers comprise a propulsion arrangement configured todrive one or more drive wheels of the lawnmower. Walk-behind mowers lacking a propulsionarrangement are sometimes referred to as “push mowers”. A riding mower is a mowercomprising a seat for a user, a steering device, such as a steering wheel, and a motorconfigured to provide motive power to the riding mower. Usually, riding mowers are used to mow bigger lawns, gardens, parks, sports fields, golf courts or the like.

Self-propelled autonomous robotic lawnmowers have become increasingly popular, partlybecause they usually are capable of performing work which previously was made manually.A self-propelled robotic lawnmower is capable of navigating in an area in an autonomousmanner, i.e. without the intervention of a user. The robotic lawnmower may move in asystematic and/or random pattern to ensure that the area is completely covered. Somerobotic lawnmowers require a user to set up a boundary wire around an area that defines thearea to be operated by the robotic lawnmower. Such robotic lawnmowers use a sensor tolocate the boundary wire and thereby the boundary of the area to be operated. When such arobotic lawnmower reaches the boundary wire, the robotic lawnmower is usually stopped andthen operated in a direction opposite to the direction of travel that the robotic lawnmower had at the time of the detection of the boundary wire.

As an alternative, or in addition, robotic lawnmowers may comprise other types of positioningunits and sensors, for example sensors for detecting an event, such as a collision with anobject within the area. Similarly, when a collision with an object is detected, the roboticlawnmower is usually stopped and then operated in a direction opposite to the direction of travel that the robotic lawnmower had at the time of the detection of the collision. 2 Traction is a problem associated with lawnmowers comprising driven wheels. Many areascomprise more or less slopes which add to the problem of traction, especially in wet conditions.

Another problem associated with robotic lawnmowers is wear and tear of the area operatedby the robotic lawnmower. As an example, wheel slip of one or more Wheels of thelawnmower may cause unwanted marks in the area operated by the lawnmower. ln addition,the presence of slopes in an area operated may significantly increase the probability of unwanted marks in the area due to an increased risk of wheel slip.

Moreover, for a robotic lawnmower, the lack of traction may adversely affect the coverage ofan area operated by the robotic lawnmower. One reason is that the lack of traction mayaffect the travelling direction of the lawnmower. That is, wheel slip of one or more Wheels ofthe robotic lawnmower may cause unexpected changes of the travel direction of the roboticlawnmower, which, due to the topography of the area, may result in that some parts of thearea are operated more frequently, and some other parts of the area are operated less frequently.

Another reason is that parts of the area comprising slope inclinations exceeding a certainslope inclination may be difficult or impossible to cut due to the lack of traction. As anexample, some manufacturers of robotic lawnmowers recommend customers to not place theboundary wire at a part of an area comprising a slope inclination of more than 15%. Thisbecause the robotic lawnmower may have problems in getting started again after havingreached and stopped at the boundary wire. However, such recommendations usually do not match demands of customers and the topology of their gardens.

A further problem associated with lawnmowers in general is the build-up of matter, such ascuttings, onto various components of the lawnmower. As an example, matter, such ascuttings, may stick to the wheels of the lawnmower and to portions of the lawnmowersurrounding the wheels. lf so, rotation of the wheels may become blocked. Moreover, build- up of matter onto a wheel may adversely affect the traction of the wheel.

Moreover, generally, on today's consumer market, it is an advantage if products, such asrobotic lawnmowers and their associated devices, have conditions and/or characteristics suitable for being manufactured and assembled in a cost-efficient manner.

SUMMARYlt is an object of the present invention to overcome, or at least alleviate, at least some of the above-mentioned problems and drawbacks.

According to a first aspect of the invention, the object is achieved by a lawnmowercomprising at least one drive wheel and a propulsion motor configured to rotate the drivewheel. The drive wheel comprises a first wheel member connected to the propulsion motorand a second wheel member comprising a ground engaging surface configured to abutagainst a ground surface during operation of the lawnmower. The drive wheel furthercomprises a number of grip enhancing members movably arranged relative to the groundengaging surface between a retracted and an extracted position. The drive wheel furthercomprises a mechanism configured to move the grip enhancing members between theretracted and the extracted position based on a torque between the first and second wheel members.

Since the mechanism is configured to move the grip enhancing members between theretracted and the extracted position based on a torque between the first and second wheelmembers, a lawnmower is provided capable of obtaining an automatic control of the positionof the grip enhancing members, and thereby also of the grip of the drive wheel, based on theneed for traction. That is, the risk of wheel slip is higher when the torque between the firstand second wheel members is high, compared to when the torque between the first andsecond wheel members is low. Thus, the grip enhancing members can be moved to theextracted position when the torque between the first and second wheel members is high, i.e.when there is a need for higher wheel grip. Likewise, the grip enhancing members can bemoved to the retracted position when the torque between the first and second wheel members is low, i.e. when the need for wheel grip is low.

As an example, if the lawnmower is mowing a flat area at constant speed and reaches anuphill slope, the gravitational force acting on the lawnmower decreases the traveling speed ofthe lawnmower. Moreover, the torque between the first and second wheel membersincreases when the lawnmower reaches the uphill slope. This because the first wheelmember is connected to the propulsion motor and the second wheel member comprises theground engaging surface. Accordingly, as a result of the increased torque between the firstand second wheel members, the mechanism can move the grip enhancing members to theextracted position. Thereby the grip of the drive wheel can be significantly enhanced, and therisk of wheel slip can thereby be significantly reduced when the lawnmower is traveling up the uphill slope. When the lawnmower is reaching a flat area, the torque between the first 4 and second wheel members decreases, and the mechanism can, as a result thereof, movethe grip enhancing members to the retracted position. Obviously, the need for traction islower when traveling on a flat area than when traveling along an uphill slope. ln this manner,an automatic control of the position of the grip enhancing members is provided based on the need for traction.

As another example, if the lawnmower is mowing a flat area at constant speed and reaches asteep downhill slope, the gravitational force on the lawnmower acts in a direction wanting toincrease the traveling speed of the lawnmower. However, since the lawnmower is controlledto operate at constant speed, or at least is provided with a maximum propulsion speed of thepropulsion motor, the torque between the first and second wheel members increases whenthe lawnmower reaches the downhill slope. This because the first wheel member isconnected to the propulsion motor and the second wheel member comprises the groundengaging surface. Thus, as a result of the increased torque between the first and secondwheel members, the mechanism can move the grip enhancing members to the extractedposition. Thereby the grip of the drive wheel can be significantly enhanced, and the risk ofwheel slip can thereby be significantly reduced when the lawnmower is traveling down theslope. ln this manner, an automatic control of the position of the grip enhancing members can be provided based on the need for traction.

As a further example, if the lawnmower is at stand still and initiates propulsion, the increasedtorque between the first and second wheel members in the start-up phase may cause themechanism to move the grip enhancing members to the extracted position. The torquebetween the first and second wheel members then decreases as the travel speed of thelawnmower increases. Thus, when the lawnmower is reaching a certain travel speed afterthe start-up phase, and travels on a sufficiently flat area, the mechanism may move the gripenhancing members to the retracted position. Obviously, the risk of wheel slip is greater atthe start-up phase of the lawnmower as compared to when the lawnmower is travelling atconstant speed along a sufficiently flat area. Thus, in this manner, an automatic control of the position of the grip enhancing members can be provided based on the need for traction.

As understood from the above, the control of the position of the grip enhancing members,based on the torque between the first and second wheel members, is particularlyadvantageous if the lawnmower is to initiate propulsion in a steep slope, for example after having stopped in a steep slope.

Accordingly, due to the features of the lawnmower according to the embodiments herein, alawnmower is provided having conditions for improved traction when needed. As a furtherresult, a lawnmower is provided capable of operating areas having greater slope inclinations.ln this manner, a lawnmower is provided capable of matching demands of customers and thetopology of their gardens. Furthermore, since the lawnmower is capable of reducing the riskof wheel slip, a lawnmower is provided having a reduced probability of making unwanted marks in the operated area.

An alternative solution to the problem of traction of the drive wheel would be to arrangestationary spikes or studs on the drive wheel. However, such a solution would significantlyincrease the risk of build-up of matter onto the drive wheel, such as for example clippings and leaves.

Since the mechanism is configured to move the grip enhancing members between theretracted and the extracted position based on the torque between the first and second wheelmembers, any matter stuck onto the grip enhancing members may be removed from the gripenhancing members when the grip enhancing members are moved to the retracted position.ln this manner, the risk of build-up of matter onto the drive wheel is significantly reduced as compared to such a solution.

Moreover, in view of a solution comprising stationary spikes or studs arranged on the drivewheel, the lawnmower can be operated with the grip enhancing members in the retractedposition when the need for traction is lower. Thereby, wear and tear of an area operated canbe reduced. Moreover, the lawnmower can be operated with the grip enhancing members inthe retracted position when traveling on hard surfaces such as pavement. ln this manner,wear and tear of the grip enhancing members and of the hard surface can be reduced.

Moreover, vibration of the lawnmower can be reduced when traveling on such surfaces.

An even further advantage with the solution according to the embodiments herein is that thegrip enhancing members may remove matter stuck onto surfaces surrounding the drivewheel, such as fenders, mudguards, and the like, when the grip enhancing members are inthe extracted position. ln this manner, it can be ensured that a clearance space is obtained around the drive wheel when the grip enhancing members are in the retracted position.

Furthermore, since the risk of wheel slip is reduced, unexpected changes of the traveldirection of the lawnmower can be avoided. Thereby, the coverage of an area operated by a lawnmower can be improved.

Accordingly, a lawnmower is provided overcoming, or at least alleviating, at least some of theabove-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

Optionally, the first wheel member is configured to rotate relative to the second wheelmember between a first and a second position based on the torque between the first andsecond wheel members. Thereby, conditions are provided for a simple and low costmechanism configured to move the grip enhancing members between the retracted and theextracted position based on the rotational position of the first wheel member relative to the second wheel member.

Optionally, the mechanism is configured to move the grip enhancing members to theretracted position upon rotation of first wheel member to the first position, and wherein thedrive wheel comprises one or more elastic members configured to bias the first wheelmember towards the first position. Thereby, the grip enhancing members can be moved tothe retracted position in a simple, reliable, and efficient manner. As a further result thereof,any matter stuck onto the grip enhancing members may be removed from the grip enhancingmembers in an efficient manner when the torque between the first and second wheel members is below a threshold torque.

Optionally, the grip enhancing members are lockable in at least one of the retracted positionand the extracted position. Thereby, a user-friendly lawnmower is provided allowing a user tolock the grip enhancing members in at least one of the retracted position and the extractedposition. As an example, a user may want to lock the grip enhancing members in theextracted position when cutting in wet conditions, when cutting less sensitive areas, whencutting undulated areas having a high proportion of steep slopes, and/or when wanting toaerate a lawn. A user may want to lock the grip enhancing members in the retracted position in dry conditions, and/or when cutting flatter areas.

Optionally, the mechanism is configured to move the grip enhancing members to theextracted position when a torque having a first torque direction rises above a first thresholdtorque, and wherein the lawnmower is accelerated in a forward direction of the lawnmowerwhen a torque having the first torque direction is applied onto the first wheel member.Thereby, a lawnmower is provided capable of improving the grip in the forward direction thereof in an efficient manner, when needed. 7 Optionally, the mechanism is configured to move the grip enhancing members to theextracted position when a torque between the first and second wheel members having asecond torque direction rises above a second threshold torque, and wherein the lawnmoweris accelerated in a reverse direction of the lawnmower when a torque having the secondtorque direction is applied onto the first wheel member. Thereby, a lawnmower is providedcapable of improving the grip in the reverse direction thereof in an efficient manner, when needed.

Optionally, one of the first and second threshold torques is lower than the other of the firstand second threshold torques. Thereby, a lower propulsion torque in one of the mowingdirections of the lawnmower is required for moving the grip enhancing members to theretracted position than what is required in the other mowing direction. As an example,according to some embodiments, the second threshold torque is lower than the firstthreshold torque. Accordingly, in such embodiments, a lower propulsion torque in the reversedirection of the lawnmower is required for moving the grip enhancing members to theextracted position than what is required in the fonNard direction of the lawnmower. Such asolution is particularly advantageous if the lawnmower is to initiate propulsion in the reversedirection in a steep slope, for example after having stopped in a steep slope. Moreover,according to such embodiments, the grip enhancing members are more likely to be moved to the extracted position when travelling in the fonNard direction down a slope.

Optionally, the mechanism is transferable to a state in which the mechanism keeps the gripenhancing members in the retracted position also when a torque is applied onto the firstwheel member in one of the first and second torque directions exceeding the respectivethreshold torque. Thereby, a user can prevent the grip enhancing members from moving tothe extracted position upon propulsion in one of the mowing directions of the lawnmower, i.e.in one of the forward direction and the reverse direction. ln this manner, a more user-friendly lawnmower is provided.

Optionally, the mechanism is configured to move the grip enhancing members in radialdirections of the drive wheel. Thereby, an enhanced grip can be provided in a simple andefficient manner. Moreover, conditions are provided for a simple and low cost mechanism for moving the grip enhancing members between the retracted and the extracted position.

Optionally, the grip enhancing members are formed as elongated rods. Thereby, anenhanced grip can be provided in a simple and efficient manner. Moreover, a drive wheel is provided having conditions and characteristics suitable for being manufactured and 8 assembled in a cost-efficient manner while being capable improving the grip in an efficient manner when needed.

Optionally, the grip enhancing members are movably arranged in through holes of thesecond wheel member. Thereby, a drive wheel is provided having conditions andcharacteristics suitable for being manufactured and assembled in a cost-efficient mannerwhile being capable improving the grip in an efficient manner when needed. As a furtherresult thereof, it may be ensured that any matter stuck onto the grip enhancing members canbe removed from the grip enhancing members in an efficient manner when the grip enhancing members are moved towards the retracted state.

Preferably, the lawnmower comprises a cleaning device configured to clean the groundengaging surface and/or the grip enhancing members during operation of the lawnmower.Such a cleaning device may for example comprise a brush arrangement comprising a brushconfigured to rotate relative to the ground engaging surface during operation of thelawnmower. The brush may comprise a brush body and a number of bristles arranged on thebrush body. The bristles may be configured to abut against the grip enhancing memberswhen the grip enhancing members are in the extracted position and the brush body isrotating. Moreover, the bristles may be configured to abut against portions of the gripenhancing members upon rotation of the brush body when the grip enhancing members arein the retracted position. Moreover, the bristles may be configured to abut against the groundengaging surface upon rotation of the brush body. ln this manner, the ground engagingsurface and/or the grip enhancing members can be cleaned during operation of thelawnmower. As a result, the risk of build-up of matter onto the drive wheel is further minimized.

Optionally, the second wheel member comprises a number of stationary friction enhancingelements protruding from the ground engaging surface, and wherein the grip enhancingmembers are arranged in areas between the stationary friction enhancing elements.Thereby, wear and tear of the grip enhancing members can be reduced when the gripenhancing members are in the retracted position. Moreover, the drive wheel may roll over ahard surface Without the grip enhancing members touching the hard surface, at least whenthe grip enhancing members are in the retracted position. Thereby, the grip enhancingmembers can be provided in a hard material, such as a metal material, without risking damage of hard surfaces and/or components of the drive wheel. 9 Optionally, the mechanism comprises a number of cam surfaces and a number of followers each abutting against a cam surface. Thereby, a simple, efficient, and reliable mechanism isprovided. As a further result, a drive wheel is provided having conditions and characteristicssuitable for being manufactured and assembled in a cost-efficient manner while being capable improving the grip in an efficient manner when needed.

Optionally, the first wheel member comprises the cam surfaces. Thereby, a simple, efficient,and reliable mechanism is provided. As a further result, a drive wheel is provided havingconditions and characteristics suitable for being manufactured and assembled in a cost- efficient manner while being capable improving the grip in an efficient manner when needed.

Optionally, one or more of the grip enhancing members is/are attached to a follower.Thereby, a simple, efficient, and reliable mechanism is provided. As a further result, a drivewheel is provided having conditions and characteristics suitable for being manufactured andassembled in a cost-efficient manner while being capable improving the grip in an efficientmanner when needed. According to some embodiments of the present disclosure, two ormore of the grip enhancing members are attached to one follower of the number of followers. ln this manner, a further simpler and more cost-efficient mechanism can be provided.

Optionally, the mechanism comprises a number of elastic members forcing the followersagainst the cam surfaces. Thereby, an abutting contact between the followers and the camsurfaces can be ensured. Moreover, the forcing of the followers against the cam surfacesmay bias the first wheel member towards a position relative to the second wheel member inwhich the grip enhancing members assume the retracted position. ln this manner, a simple,efficient, and reliable mechanism is provided. As a further result, a drive wheel is providedhaving conditions and characteristics suitable for being manufactured and assembled in acost-efficient manner while being capable improving the grip in an efficient manner when needed.

Optionally, the cam surfaces are curve-shaped in a plane perpendicular to a rotation axis ofthe drive wheel. Thereby, a simple, efficient, and reliable mechanism is provided. As a furtherresult, a drive wheel is provided having conditions and characteristics suitable for beingmanufactured and assembled in a cost-efficient manner while being capable improving the grip in an efficient manner when needed.

Optionally, the curve-shape of the cam surfaces is arranged such that an actuation speed of the grip enhancing members is higher close to the retracted position than the actuation speed close to the extracted position. ln this manner, the grip enhancing members can bemoved in a quick manner from the retracted position and with a greater force as theyapproach the extracted position. The higher actuation speed close to the retracted positionmay be obtained by arranging the cam surfaces in such a manner that the followers abutagainst portions of the cam surfaces having steeper angles relative to tangentia| directions ofthe drive wheel when the grip enhancing members are close to the retracted position as compared to when the grip enhancing members are close to the extracted position.

Optionally, the cam surfaces are arc-shaped in a plane perpendicular to a rotation axis of thedrive wheel. Thereby, a simple, efficient, and reliable mechanism is provided. As a furtherresult, a drive wheel is provided having conditions and characteristics suitable for beingmanufactured and assembled in a cost-efficient manner while being capable improving thegrip in an efficient manner when needed. Moreover, the arc-shaped cam surfaces mayensure that an actuation speed of the grip enhancing members is higher close to theretracted position than the actuation speed close to the extracted position. ln this manner,the grip enhancing members can be moved in a quick manner from the retracted position and with a greater force as they approach the second position.

Optionally, the drive wheel comprises the same number of cam surfaces as the number offollowers. Thereby, a simple, efficient, and reliable mechanism is provided. As a furtherresult, a drive wheel is provided having conditions and characteristics suitable for beingmanufactured and assembled in a cost-efficient manner while being capable improving the grip in an efficient manner when needed.

Optionally, a follower of the number of followers is configured to assume a position bet\Neentwo adjacent cam surfaces when the torque between the first and second wheel members isbelow a threshold torque. Thereby, a simple, efficient, and reliable mechanism is providedhaving conditions for moving the grip enhancing members to the extracted position based onthe torque between the first and second wheel members in two torque directions. As a furtherresult, a drive wheel is provided having conditions and characteristics suitable for beingmanufactured and assembled in a cost-efficient manner while being capable improving the grip in an efficient manner when needed.

Optionally, the cam surfaces are arranged such that the followers are closer to an rotationaxis of the drive wheel when the torque between the first and second wheel members isbelow a threshold torque, than when the torque between the first and second wheel members exceeds the threshold torque. Thereby, a simple, efficient, and reliable mechanism 11 is provided. As a further result, a drive wheel is provided having conditions andCharacteristics suitable for being manufactured and assembled in a cost-efficient manner while being capable improving the grip in an efficient manner when needed.

Optionally, the mechanism comprises a plurality of arms arranged between the first andsecond wheel members, and wherein at least a number of the plurality of arms areconfigured to move based on the torque between the first and second wheel members so asto cause the movement of the grip enhancing members between the retracted and theextracted position. Thereby, a simple, efficient, and reliable mechanism is provided. As afurther result, a drive wheel is provided having conditions and characteristics suitable forbeing manufactured and assembled in a cost-efficient manner while being capable improving the grip in an efficient manner when needed.

Optionally, at least a number of the plurality of arms are configured to be subjected to elasticdeformation when the torque between the first and second wheel members rises above athreshold torque. Thereby, a simpler and more reliable mechanism can be providedcircumventing the need for hinges, cam surfaces, and the like. As a further result, a drivewheel is provided having conditions and characteristics suitable for being manufactured andassembled in a cost-efficient manner while being capable improving the grip in an efficient manner when needed.

Optionally, the mechanism is a compliant mechanism. Thereby, a simpler and more reliablemechanism can be provided circumventing the need for hinges, cam surfaces, and the like.As a further result, a drive wheel is provided having conditions and characteristics suitablefor being manufactured and assembled in a cost-efficient manner while being capable improving the grip in an efficient manner when needed.

Optionally, the lawnmower is a self-propelled robotic lawnmower. Thereby, a roboticlawnmower is provided capable of obtaining an automatic control of the position of the gripenhancing members, and thereby also of the grip of the drive wheel, based on the need for traction in a simple and efficient manner.

Moreover, as understood from the herein described, the control of the position of the gripenhancing members based on the torque between the first and second wheel members isparticularly advantageous if the robotic lawnmower is to initiate propulsion in a steep slope, for example after having stopped at a boundary wire positioned in a steep slope. 12 Moreover, since the robotic lawnmower has conditions for improved traction, a roboticlawnmower is provided capable of operating areas having greater slope inclinations. ln thismanner, the robotic lawnmower allows for the placement of boundary wires in slopes havinggreater a slope inclinations than would be possible otherwise. ln this manner, a roboticlawnmower is provided capable of matching demands of customers and the topology of their gardens.

Furthermore, since the risk of wheel s|ip is reduced, unexpected changes of the traveldirection of the robotic lawnmower can be avoided. Thereby, the coverage of an area operated by a robotic lawnmower can be improved.

Moreover, in view of a solution comprising stationary spikes or studs arranged on the drivewheel, the robotic lawnmower can be operated with the grip enhancing members in theretracted position when trave|ing on hard surfaces such as pavement or the top surface of acharging station. ln this manner, wear and tear of the grip enhancing members and of thehard surface can be reduced. Moreover, vibration of the robotic lawnmower can be reduced when trave|ing on such surfaces.

Optionally, the lawnmower comprises a control arrangement configured to control operationof the propulsion motor, and wherein the control arrangement is configured to selectivelyperform a control operation in which the propulsion motor is controlled to apply a torque ontothe first wheel member causing a movement of the grip enhancing members towards theextracted position. Thereby, a lawnmower is provided capable of actively moving the gripenhancing members to the retracted position. As a result, the grip can be improved whendetermined necessary, for example based on input data. Thereby, lawnmower is providedhaving improved conditions for navigating in areas having a high risk of wheel s|ip, such as undulated areas.

Optionally, the control arrangement is configured to determine whether to perform the controloperation based on input data. Thereby, a lawnmower is provided capable of actively movingthe grip enhancing members to the retracted position based on input data. Thereby, alawnmower is provided having further improved conditions for navigating in areas having a high risk of wheel s|ip, such as undulated areas.

Optionally, the input data is representative of a current or impending slope inclination at thelocation of the lawnmower and/or a current or impending inclination angle of the lawnmower.

Thereby, a lawnmower is provided having improved conditions for operating in steep slopes. 13 That is, if the data indicates presence of a current or impending slope inclination exceeding athreshold inclination, the control arrangement may perform the control operation to activelymove the grip enhancing members to the extracted position. Thereby, the grip is significantly improved and the risk of wheel s|ip in the slope is significantly reduced.

Optionally, the input data is representative of one or more of traction conditions at thelocation of the lawnmower, weather conditions at the location of the lawnmower, andhumidity at the location of the lawnmower. Thereby, a lawnmower is provided having improved conditions for operating under conditions with increased risk of wheel s|ip.

Optionally, the input data is representative of presence of wheel s|ip of one or more wheelsof the lawnmower. Thereby, a lawnmower is provided capable of actively improving the gripof the drive wheel in case wheel s|ip of one or more wheels of the lawnmower is detected.Thereby, a lawnmower is provided having improved conditions for navigating in areas having a high risk of wheel s|ip, such as undulated areas.

Optionally, the control operation comprises stopping the lawnmower before controlling thepropulsion motor to apply the torque onto the first wheel member. Thereby, a lawnmower isprovided having further improved conditions for regaining grip after wheel s|ip of one or morewheels of the lawnmower is detected. This because it is ensured that the ground engagingsurface of the second wheel member is stationary relative to the ground surface beforeinitiating propulsion. Thereby, a lawnmower is provided having further improved conditionsfor navigating in areas having a high risk of wheel s|ip, such as undulated areas. Moreover, the risk of unwanted marks in the operated area is reduced.

According to a second aspect of the invention, the object is achieved by a drive wheel for alawnmower, wherein the lawnmower comprises a propulsion motor configured to rotate thedrive wheel. The drive wheel comprises a first wheel member configured to be connected tothe propulsion motor of the lawnmower and a second wheel member comprising a groundengaging surface configured to abut against a ground surface during operation of thelawnmower. The drive wheel further comprises a number of grip enhancing membersmovably arranged relative to the ground engaging surface between a retracted and anextracted position. The drive wheel further comprises a mechanism configured to move thegrip enhancing members bet\Neen the retracted and the extracted position based on a torque between the first and second wheel members. 14 Since the mechanism is configured to move the grip enhancing members between theretracted and the extracted position based on a torque between the first and second wheelmembers, a drive wheel is provided capable of obtaining an automatic control of the positionof the grip enhancing members, and thereby also of the grip of the drive wheel, based on the need for traction.

Accordingly, a drive wheel is provided overcoming, or at least alleviating, at least some of theabove-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

The drive wheel according to the second aspect of the invention is combinable with any oneof the features of the drive wheel of the lawnmower according to the first aspect of theinvention. That is, the drive wheel according to the second aspect of the invention maycomprise one or more of the features, functions, and advantages of the drive wheel of the lawnmower described herein.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGSVarious aspects of the invention, including its particularfeatures and advantages, will bereadily understood from the example embodiments discussed in the following detailed description and the accompanying drawings, in which: Fig. 1 schematically illustrates a lawnmower according to some embodiments, Fig. 2 illustrates a perspective view of a drive wheel of the lawnmower illustrated in Fig. 1,Fig. 3 illustrates a perspective view of a first wheel member of the drive wheel illustrated inFig. 2, Fig. 4 illustrates a perspective view of a second wheel member of the drive wheel illustratedin Fig. 2, Fig. 5 illustrates the first wheel member illustrated in Fig. 3 rotated to a second position,Fig. 6 illustrates the second wheel member illustrated in Fig. 4 with grip enhancing membersin an extracted position, Fig. 7 illustrates a drive wheel according to some further embodiments of the presentdisclosure, and Fig. 8 illustrates the drive wheel illustrated in Fig. 7 with a first wheel member rotated to a second position.

DETAILED DESCRIPTIONAspects of the present invention will now be described more fully. Like numbers refer to likeelements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.

Fig. 1 schematically illustrates a lawnmower 1 according to some embodiments. According tothe illustrated embodiments, the lawnmower 1 is a self-propelled autonomous roboticlawnmower 1 capable of navigating and cutting grass in an autonomous manner in an areawithout the intervention or the control of a user. For the reason of brevity and clarity, the self-propelled autonomous robotic lawnmower 1 is in some places herein referred to as “therobotic lawnmower 1” or simply the “lawnmower 1”. According to the illustrated embodiments,the robotic lawnmower 1 is configured to be used to cut grass in areas used for aesthetic andrecreational purposes, such as gardens, parks, city parks, sports fields, lawns around houses, apartments, commercial buildings, offices, and the like.

According to further embodiments of the present disclosure, the lawnmower 1, as referred toherein, may be another type of lawnmower 1, such as a walk-behind mower or a riding mOWGF.

The lawnmower1 comprises a lawnmower chassis 2 and a number of wheels 3, 6 supportingthe lawnmower chassis 2 by abutting against a ground surface 22 during operation of thelawnmower 1. ln Fig. 1, only two wheels 3, 6 are visible. However, according to the illustratedembodiments, the lawnmower1 comprises four wheels 3, 6, namely two drive wheels 3 andtwo support wheels 6. The drive wheels 3 of the lawnmower 1 may each be powered by apropulsion motor 4 of the lawnmower 1 to provide motive power and/or steering of thelawnmower 1. The lawnmower1 may thus comprise one propulsion motor 4 per drive wheel3, wherein the propulsion motor/motors 4 is/are configured to rotate a drive wheel 3. Thelawnmower 1 may comprise a transmission between the respective propulsion motor 4 and drive wheel 3. The propulsion motor/motors 4 may comprise an electrical motor. ln Fig. 1, a longitudinal direction ld of the lawnmower1 is indicated. The longitudinal directionld of the lawnmower 1 extends in a longitudinal plane LP of the lawnmower 1. Thelongitudinal plane LP is parallel to a ground surface 22 when the lawnmower1 is positionedin an intended use position onto a flat ground surface 22, as illustrated in Fig. 1. Moreover,the longitudinal direction ld of the lawnmower 1 is parallel to a fonNard direction fd of travel of the lawnmower 1 as well as a reverse direction rd of travel of the lawnmower 1, as is further 16 explained herein. Also, in Fig. 1, a horizontal plane hp at the location of the lawnmower 1 is indicated.

According to the illustrated embodiments, the drive wheels 3 of the lawnmower 1 are non-steered Wheels having a fix rolling direction in relation to the lawnmower chassis 2. Therespective rolling direction of the drive wheels 3 of the lawnmower 1 is substantially parallelto the longitudinal direction ld of the lawnmower 1. According to the illustrated embodiments,the support Wheels 6 are non-driven Wheels. Moreover, according to the illustratedembodiments, the support wheels 6 can pivot around a respective pivot axis such that therolling direction of the respective support wheel 6 can follow a travel direction of the lawnmower 1.

As understood from the above, when the drive wheels 3, 6 of the lawnmower 1 are rotated atthe same rotational velocity in a fonNard rotational direction, and no wheel slip is occurring,the lawnmower 1 will move in the fonNard direction fd indicated in Fig. 1. Likewise, when thedrive wheels 3, 6 of the lawnmower 1 are rotated at the same rotational velocity in a reverse rotational direction, and no wheel slip is occurring, the lawnmower1 will move in the reverse direction rd indicated in Fig. 1. The reverse direction rd is opposite to the fonNard direction fd.

According to the illustrated embodiments, the lawnmower 1 may be referred to as a four-Wheeled rear wheel driven lawnmower 1. According to further embodiments, the lawnmower1 may be provided with another number of wheels 3, 6, such as three wheels. Moreover,according to further embodiments, the lawnmower 1 may be provided with anotherconfiguration of driven and non-driven Wheels, such as a front wheel drive or an all-wheel drive.

The lawnmower 1 comprises a cutting unit 10 configured to cut vegetation during operationof the lawnmower 1. According to the illustrated embodiments, the cutting unit 10 comprisesa cutting disc provided With a number of cutting members arranged at a periphery of thecutting disc. Moreover, the lawnmower 1 comprises a motor configured to rotate the cuttingunit 10. The motor may comprise an electric motor. The motor is not illustrated in Fig. 1 forthe reason of brevity and clarity. According to the illustrated embodiments, the cutting unit 10is configured to rotate in a cutting plane substantially parallel to the longitudinal plane LP ofthe lawnmower 1. The angle between the cutting plane and the longitudinal plane LP may be less than 7 degrees. 17 As indicated in Fig. 1, the drive wheel 3 comprises a first wheel member 5 and a secondwheel member 7. The first wheel member 5 is connected to the propulsion motor 4. Asindicated above, the first wheel member 5 may be connected to the propulsion motor 4 via atransmission, or the like. The second wheel member 7 comprises a ground engaging surface7'. The ground engaging surface 7' is configured to abut against a ground surface 22 duringoperation of the lawnmower 1. The ground engaging surface 7' may also be referred to as aro||ing surface 7' of the drive wheel 3. This because the ground engaging surface 7' is configured to roll against the ground surface 22 during operation of the lawnmower 1.

Fig. 2 illustrates a perspective view of a drive wheel 3 of the lawnmower 1 illustrated in Fig.1. The drive wheel 3 is configured to rotate around a rotation axis ax during operation of thelawnmower 1. The rotation axis ax is also indicated in Fig. 1. The drive wheel 3 comprises anumber of grip enhancing members 8. The grip enhancing members 8 are movably arrangedrelative to the ground engaging surface 7' between a retracted and an extracted position. lnFig. 2, the grip enhancing members 8 are illustrated in the retracted position. The drive wheel3 further comprises a mechanism 9 configured to move the grip enhancing members 8between the retracted position and the extracted position based on a torque betvveen the first and second wheel members 5, 7, as is further explained herein. ln more detail, according to the illustrated embodiments, the first wheel member 5 isconfigured to rotate relative to the second wheel member 7 between a first and a secondposition based on the torque between the first and second wheel members 5, 7. Moreover,the mechanism 9 is configured to move the grip enhancing members 8 to the retractedposition upon rotation of first wheel member 5 to the first position and is configured to movethe grip enhancing members 8 to the extracted position upon rotation of first wheel member 5 to the second position, as is further explained herein.

Fig. 3 illustrates a perspective view of the first wheel member 5 of the drive wheel 3illustrated in Fig. 2. As can be seen in Fig. 3, the first wheel member 5 comprises a shaftinterface 14 for the connection to a drive shaft. The drive shaft may thus be connected to thepropulsion motor 4 indicated in Fig. 1, for example via a transmission. According to theillustrated embodiments, the mechanism 9 comprises a number of cam surfaces 11 and anumber of followers 13. As seen in Fig. 3, according to the illustrated embodiments, the firstwheel member 5 comprises the cam surfaces 11. Moreover, according to the illustratedembodiments, the mechanism 9 comprises the same number of cam surfaces 11 as thenumber of followers 13. That is, according to the illustrated embodiments, the mechanism 9 comprises six cam surfaces 11 and six followers 13. According to further embodiments, the 18 mechanism 9 may comprise another number of cam surfaces 11 and followers 13, such as a number between three and twenty. ln Fig. 3, the followers 13 are illustrated in positions corresponding to positions obtainedwhen the drive wheel is in the assembled state and the grip enhancing members 8 are in theretracted state. As indicated above, the first wheel member 5 is in the first position relative tothe second wheel member when the grip enhancing members 8 are in the retracted state.The followers 13 have been included in Fig. 3 to improve understanding of the operatingprinciple of the mechanism 9. As seen in Fig. 3, according to the illustrated embodiments, thegrip enhancing members 8 are attached to the followers 13. ln more detail, according to theillustrated embodiments, two grip enhancing members 8 are attached to one follower 13.According to further embodiments, another number of grip enhancing members 8 may be attached to each follower 13, such as one, three, four, or the like.

Fig. 4 i||ustrates a perspective view of the second wheel member 7 of the drive wheel 3illustrated in Fig. 2. ln Fig. 4, the followers 13 are illustrated in positions corresponding topositions obtained When the drive Wheel is in the assembled state and the grip enhancingmembers 8 are in the retracted state, i.e. when the first wheel member 5 is in the first positionrelative to the second wheel member 7. As seen in Fig. 4, the grip enhancing members 8 aremovably arranged in through ho|es 17 of the second Wheel member 7. According to theillustrated embodiments, the through ho|es 17 of the second wheel member 7 are providedthrough the ground engaging surface 7' of the drive wheel. The through ho|es 17 areprovided in directions substantially coinciding with radia| directions R of the drive wheel.Moreover, as seen in Fig. 2 - Fig. 4, according to the illustrated embodiments, the gripenhancing members 8 are formed as e|ongated rods. Therefore, the grip enhancingmembers 8, as referred to herein, may also be referred to as studs 8. According to theillustrated embodiments, the followers 13 are slidably arranged in radia| directions R of thedrive wheel in pockets 18 of the second wheel member 7. Thus, according to the illustratedembodiments, the followers 13 are rotationally locked in relation to the second wheelmember 7 and the cam surfaces 11 are rotationally locked in relation to the first wheel member 5.

As indicated in Fig. 3 and Fig. 4, the mechanism 9 comprises a number of elastic members15. The elastic members 15 are configured to force the followers 13 against the camsurfaces 11. As can be seen in Fig. 3 and Fig. 4, according to the illustrated embodiments,the mechanism 9 comprises one elastic member 15 per follower 13, wherein the elastic member 15 is attached to the follower 13. The elastic member 15 and the follower 13 may be 19 provided in one piece of continuous material, such as a polymeric material. According to theillustrated embodiments, elastic members 15 are formed as a respective leaf spring abuttingagainst a radially inner surface of the second wheel member 7. According to furtherembodiments, the elastic members 15 may comprise a coi| spring, or the like. The gripenhancing members 8 may be provided in a metal material, such as a steel material. Due tothese features, the drive wheel can be manufactured and assembled in a cost-efficient manner while being capable of significantly enhancing the grip, as is further explained herein.

Moreover, according to the illustrated embodiments, each follower 13 of the number offollowers 13 is configured to assume a position between two adjacent cam surfaces 11 whenthe grip enhancing members 8 are in the retracted state, i.e. when the first wheel member 5is in the first position relative to the second wheel member 7. ln Fig. 3, the followers 13 areillustrated in such positions. Moreover, as is clearly seen in Fig. 3, the cam surfaces 11 arearranged such that the followers 13 are closer to an rotation axis ax of the drive wheel 3when the grip enhancing members 8 are in the retracted state, than when the grip enhancing members 8 are in the extracted state.

According to the illustrated embodiments, the cam surfaces 11 are arc-shaped in a plane Pperpendicular to a rotation axis ax of the drive wheel. As is further explained herein,according to further embodiments, the cam surfaces 11 may have another curve-shape in the plane P perpendicular to the rotation axis ax of the drive wheel.

Fig. 5 illustrates the first wheel member 5 illustrated in Fig. 3 rotated to the second position.ln relation to Fig. 3, the first wheel member 5 has been rotated clockwise in Fig. 5 from thefirst position to the second position relative to a second wheel member. As is clearly seen inFig. 5, the cam surfaces 11 are arranged such that the followers 13, and thus also the gripenhancing members 8, are located further from the rotation axis ax of the drive wheel 3 whenthe first wheel member 5 is in the second position, than when the first wheel member 5 is inthe first position as illustrated in Fig. 3. The followers 13 have been included in Fig. 5 to improve understanding of the operating principle of the mechanism 9.

Fig. 6 illustrates the second wheel member 7 illustrated in Fig. 4 with the grip enhancingmembers 8 in the extracted position. That is, in relation to the second wheel member 7illustrated in Fig. 4, the grip enhancing members 8 have been moved to the extractedposition by the abutting contact betvveen the cam surfaces 11 and the followers 13. Thus, themechanism 9 is configured to move the grip enhancing members 8 to the extracted position upon rotation of first wheel member 5 to the second position relative to the second wheel member 7. Moreover, as can be seen in Fig. 6, the elastic members 15 have beencompressed as a result of the movement of the grip enhancing members 8 to the extracted position.

Since the elastic members 15 are configured to force the followers 13 against the camsurfaces 11, the elastic members 15 apply a counter torque betvveen the first and secondwheel members 5, 7 acting to displace the first wheel member 5 towards the first positionrelative to the second wheel member 7 when the first wheel member 5 is in a positionbetween the first and second positions. ln other words, according to the illustratedembodiments, the elastic members 15 are configured to bias the first wheel member 5towards the first position. The number of elastic members 15, the spring coefficients thereof,and the profile of the cam surfaces 11 thus determines the torque which has to be overcomein order to displace the first wheel member 5 towards the second position so as to move thegrip enhancing members 8 to the extracted position. The torque referred to in the previous sentence is in some places herein also referred to as a threshold torque.

Below, simultaneous reference is made to Fig. 1 - Fig. 6, if not indicated otherwise. ln Fig. 1,a first and a second torque direction Td1, Td2 are indicated. The lawnmower 1 is acceleratedin a forward direction fd of the lawnmower 1 when a torque having the first torque directionTd1 is applied onto the first wheel member 5. The first torque direction Td1 thus coincideswith the fon/vard rotational direction of the drive wheel 3, as referred to above. The secondtorque direction Td2 is opposite to the first torque direction Td1. Accordingly, the lawnmower1 is accelerated in a reverse direction rd of the lawnmower 1 when a torque having thesecond torque direction Td2 is applied onto the first wheel member 5. The second torquedirection Td2 thus coincides with the reverse rotational direction of the drive wheel 3, as referred to above.

According to embodiments herein, the mechanism 9 is configured to move the gripenhancing members 8 to the extracted position when a torque having a first torque directionTd1 rises above a first threshold torque. The number of elastic members 15, the springcoefficients thereof, and the profile of the cam surfaces 11 thus determines the magnitude ofthe first threshold torque. Accordingly, when the propulsion motor 4 of the lawnmower 1applies a torque onto the first wheel member 5 in the first torque direction Td1 exceeding thefirst threshold torque, the first wheel member 5 is rotated from the first position, as illustratedin Fig. 3, to the second position, illustrated in Fig. 5. As a result the grip enhancing members8 are displaced from the retracted position, as illustrated in Fig. 3, to the extracted position,illustrated in Fig. 5. 21 As indicated in Fig. 2 - Fig. 6, the mechanism 9 is configured to move the grip enhancingmembers 8 in radial directions R of the drive wheel 3. The grip enhancing members 8 aredistributed around the circumference of the ground engaging surface 7' of the second wheelmember 7 of the drive wheel 3. Since the grip enhancing members 8 protrudes further outfrom the ground engaging surface 7' when in the extracted position, the grip of the drivewheel 3 is significantly improved. Moreover, as seen in Fig. 2, Fig. 4 and Fig. 6, the secondwheel member 7 comprises a number of stationary friction enhancing elements 19 protrudingfrom the ground engaging surface 7”. As indicated in Fig. 2, according to the i||ustratedembodiments, the grip enhancing members 8 are arranged in areas 23 between thestationary friction enhancing elements 19. Thereby, wear and tear of the grip enhancingmembers 8 can be reduced when the grip enhancing members 8 are in the retractedposition. Moreover, the drive wheel 3 may roll over a hard surface without the grip enhancingmembers 8 touching the hard surface, at least when the grip enhancing members 8 are in the retracted position.

According to the i||ustrated embodiments, the lawnmower 1 comprises a control arrangement21. The control arrangement 21 is configured to control operation of the propulsion motor 4.The control arrangement 21 may be configured to selectively perform a control operation inwhich the propulsion motor 4 is controlled to apply a torque onto the first wheel member 5 inthe first torque direction Td1 or the second torque direction Td2 exceeding the first threshold torque or a second threshold torque, as is further explained herein. ln Fig. 1, the lawnmower 1 is i||ustrated as positioned onto a flat ground surface 22 beingsubstantially parallel to a horizontal plane hp at the location of the lawnmower 1. When thelawnmower 1 is travelling on a flat ground surface 22 at a constant velocity in the forwarddirection fd of the lawnmower 1, the torque bet\Neen the first and second wheel members 5,7 is likely to be below the first threshold torque. This because the second wheel member 7,which comprises the ground engaging surface 7', is rotating with the first wheel member 5 ata constant speed. However, if the lawnmower 1 is reaching a steep uphill slope, thegravitational force acting on the lawnmower 1 increases the torque between the first andsecond wheel members 5, 7. As a result thereof, the torque between the first and secondwheel members 5, 7 may rise above the first threshold torque. lf so, the mechanism 9 willmove the grip enhancing members 8 to the extracted position, as explained above. Thereby,the grip of the drive wheel 3 can be significantly improved when needed, i.e. such as when traveling up the uphill slope. 22 The first threshold torque may be set to a level such that the grip enhancing members 8 aremoved to the extracted position when the lawnmower 1 is travelling at constant velocity upan uphill slope having a certain slope inclination. Purely as an example, the first thresholdtorque may be set to a level such that the grip enhancing members 8 are moved to theextracted position when the lawnmower 1 is travelling at constant velocity up an uphill slope having a slope inclination within the range of 7-13 degrees.

Moreover, as understood from the above, in a start-up phase of the lawnmower 1 when thepropulsion motor applies a torque onto the first wheel member 5 and the lawnmower 1 isaccelerated, the torque between the first and second wheel members 5, 7 is higher thanwhen travelling at constant speed. This because the second wheel member 7, whichcomprises the ground engaging surface 7', is stationary relative to the ground surface 22when initiating propulsion. The first threshold torque may be set to a sufficiently high levelsuch that the lawnmower 1 can initiate propulsion in the fonNard direction fd when starting ona flat ground surface 22 without causing movement of the grip enhancing members 8 to theextracted position. ln this manner, a control arrangement 21 of the lawnmower 1 can selectwhether to move the grip enhancing members 8 to the extracted position in a start-up phaseof the lawnmower 1 by selecting the magnitude of the torque applied onto the first wheel member 5. ln summary, in Fig. 3, the followers 13 are illustrated in positions corresponding to positionsobtained when the drive wheel 3 is in the assembled state and the first wheel member 5 is inthe first position relative to the second wheel member 7. ln Fig. 5, the followers 13 areillustrated in positions corresponding to positions obtained when the drive wheel 3 is in theassembled state and the first wheel member 5 is in the second position relative to the secondwheel member 7. Moreover, as mentioned above, each follower 13 is in a position bet\Neentwo adjacent cam surfaces 11 when the first wheel member 5 is in the first position relative to the second wheel member 7, as seen in Fig. 3.

According to the illustrated embodiments, the first wheel member 5 is rotationally arrangedrelative to the second wheel member 7 in an opposite rotational direction from the firstposition towards a third position. The difference betvveen the second and third position is thatthe followers 13 are abutting against different cam followers 11 when the first wheel member3 is rotated towards the third position than when the first wheel member 3 is rotated towardsthe second position. Thus, according to the illustrated embodiments, each follower 13 isconfigured to cooperate with two adjacent cam surfaces 11 during operation of a lawnmower 1 comprising the drive wheel 3. ln relation to the position of the first wheel member 5 23 illustrated in Fig. 3, the first wheel member 5 rotates counterclockwise from the first positiontowards the third position. The wording clockwise and counterclockwise as used herein onlyconstitutes examples, as understood by a person skilled in the art, because the rotationaldirection of the first wheel member 5 relative to the second wheel member 7 depends theside of the lawnmower 1 at which the drive wheel 3 is intended to be arranged. The thirdposition is similar to the second position, illustrated in Fig. 5 in the sense that the followers 13are displaced in radia| directions R towards top surfaces of cam surfaces 11 when the first wheel member 5 is rotated towards the third position.

As understood from the above, the mechanism 9 is configured to move the grip enhancingmembers 8 to the extracted position when a torque between the first and second wheelmembers 5, 7 having a second torque direction Td2 rises above the second threshold torque.The number of elastic members 15, the spring coefficients thereof, and the profile of the camsurfaces 11 thus determines the magnitude of the second threshold torque. Accordingly,when the propulsion motor 4 of the lawnmower 1 applies a torque onto the first wheelmember 5 in the second torque direction Td2 exceeding the second threshold torque, thefirst wheel member 5 is rotated from the first position, as illustrated in Fig. 3, to the thirdposition. As a result, the grip enhancing members 8 are displaced from the retracted position towards the extracted position.

According to the illustrated embodiments, the cam surfaces 11 arranged on either side of thefollowers 13 comprise the same cam profile shapes, meaning that, according to theillustrated embodiments, the first and second threshold torques have the same magnitude.According to further embodiments, the cam surfaces 11 arranged on either side of thefollowers 13 may be provided with different cam profile shapes. ln this manner, one of thefirst and second threshold torques can be made lower than the other of the first and second threshold torques.

According to some embodiments of the present disclosure, the second threshold torque islower than the first threshold torque. Thereby, a lower torque applied onto the first wheelmember 5 in the second torque direction Td2 is required for moving the grip enhancingmembers 8 to the extracted position than what is required moving the grip enhancingmembers 8 to the extracted position when a torque is applied onto the first wheel member 5in the first torque direction Td1. Such a solution is particularly advantageous if thelawnmower 1 is to initiate propulsion in the reverse direction rd up a steep uphill slope, for example after having stopped in such a slope. 24 As indicated in Fig. 3 - Fig. 6, the drive wheel 3 comprises a rotation limiting assembly 24,26. The rotation limiting assembly 24, 26 is configured to lock the first wheel member 5 fromrotating relative to second wheel member 7 past the second position and past the thirdposition. According to the illustrated embodiments, the rotation limiting assembly 24, 26comprises a number of protrusions 24 arranged on the first wheel member 5 and a numberof arc-shaped slots 26 arranged on the second wheel member 7. According to furtherembodiments, the number of protrusions 24 may be arranged on the second wheel member7 and a number of arc-shaped slots 26 may be arranged on the first wheel member 5. Eachprotrusion 24 of the number of protrusion 24 extends into a slot 26 of the number of arc-shaped slots 26 when the drive wheel 3 is in an assembled state. Each slot 26 of the numberof arc-shaped slots 26 comprises a first and a second stop surface 31, 32. The protrusions24 are configured to abut against a first stop surface 31 of the slots 26 when the first wheelmember 5 is in the second position relative to the second wheel member 7. ln this manner,the first wheel member 5 is prevented from rotating past the second position. The protrusions24 are configured to abut against a second stop surface 32 of the slots 26 when the firstwheel member 5 is in the third position relative to the second wheel member 7. ln thismanner, the first wheel member 5 is prevented from rotating past the third position.According to the illustrated embodiments, the rotation limiting assembly 24, 26 comprisesfour slots 26 and four protrusions 24. According to further embodiments, the rotation limitingassembly 24, 26 may comprise another number of slots 26 and protrusions 24, such as one, two, three, five, or the like.

Moreover, according to further embodiments, the rotation limiting assembly 24, 26 maycomprise other types of components or structures than slots 26 and protrusions 24 forpreventing rotation the first wheel member 5 relative to second wheel member 7 past the second position and past the third position.

According to still further embodiments, the drive wheel 3 may lack a rotation limitingassembly. According to such embodiments, the first wheel member 5 can be rotated relativeto the second Wheel member 7 with the grip enhancing members 8 in the extracted position,with the only limitation being the abutting force of the followers 13 against the cam surfaces11. ln this manner, a pulsating force can be applied onto a ground surface 22 via the groundengaging surface 7' and the grip enhancing members 8 upon rotation of the first wheelmember 5 relative to the second wheel member 7. Such a pulsating force can facilitate takeoff of the lawnmower 1. ln addition, according to such embodiments, wheel slip of the groundengaging surface 7' and the grip enhancing members 8 relative to the ground surface 22 can be further avoided.

According to some embodiments herein, the lawnmower 1 comprises a locking assemblyallowing a locking of the grip enhancing members 8 in at least one of the retracted positionand the extracted position. Such a locking assembly may comprise means for locking the firstwheel member 5 in one or more of the first, second, and third positions relative to the secondwheel member 7. As an example, such a locking assembly may comprise one or morefastening elements screwed into the protrusions 24 of the rotation limiting assembly 24, 26which can be tightened in order to lock the first wheel member 5 from rotating relative to thesecond wheel member 7. According to further embodiments, the mechanism 9 is transferableto a state in which the mechanism 9 keeps the grip enhancing members 8 in the retractedposition also when a torque is applied onto the first wheel member 5 in one of the first andsecond torque directions Td1, Td2 exceeding the respective threshold torque. Thereby, auser can prevent the grip enhancing members 8 from moving to the extracted position upon propulsion in one of the forward direction fd and the reverse direction rd of the lawnmower 1.

Due to the arc-shape of the cam surfaces 11, according to the illustrated embodiments, thetorque applied to the first wheel member 5 towards the first position by the engagementbetween the followers 13 and the cam surfaces 11 is higher when the first wheel member 5is in a region close to the first position than when the first wheel member 5 is in a region ofthe second or third positions. ln fact, due to the arc-shape of the cam surfaces 11, the torqueapplied to the first wheel member 5 towards the first position gradually decreases uponrotation of the first wheel member 5 from the first position towards any of the second or thirdpositions. Moreover, due to the arc-shape of the cam surfaces 11, according to the illustratedembodiments, an actuation speed of the grip enhancing members 8 is higher close to theretracted position than the actuation speed close to the extracted position. ln this manner,the grip enhancing members 8 can be moved in a quick manner from the retracted position and with a greater force as they approach the extracted position.

Moreover, as indicated herein, according to the illustrated embodiments, the followers 13 arepositioned at a top surface of a cam surface 11 when the first wheel member 5 is in the firstposition relative to the second wheel member 7, as well as when the first wheel member 5 isin the third position relative to the second wheel member 7. Thereby, substantially no torqueis applied to the first wheel member 5 towards the first position by the engagement betweenthe followers 13 and the cam surfaces 11 when the first wheel member 5 is in the second orthird position. As a result, the grip enhancing members 8 can be kept in the extractedposition until the propulsion motor applies a torque onto the first wheel member 5 in a direction from the second or third positions towards the first position. 26 According to further embodiments herein, the rotation limiting assembly 24, 26 may bearranged such that the followers 13 are positioned at other portions of the cam surfaces 11,than the top surfaces thereof, when the first wheel member 5 is in the first or third positions.Moreover, as previously mentioned, the cam surfaces 11 may be provided with other camprofiles than arc-shaped cam profiles. The cam surfaces 11 of the mechanism 9 maycomprise one or more sections in which substantially no torque is applied to the first wheelmember 5 towards the first position by the engagement between the followers 13 and thecam surfaces 11. Such one or more sections may comprise a recess, a dent, a flat section,or the like, resulting in substantially no torque applied to the first wheel member 5 towardsthe first position when a follower 13 is biased against the section. ln this manner, the gripenhancing members 8 can be kept in an extracted position, or in a partially extractedposition, until the propulsion motor applies a torque onto the first wheel member 5 in a direction from the current position.

Fig. 7 illustrates a drive wheel 3 according to some further embodiments of the presentdisclosure. The drive wheel 3 illustrated in Fig. 7 may comprise the same features, functions,and advantage as the drive wheel 3 explained with reference to Fig. 1 - Fig. 6, with some differences explained below. Also some mutual features will be explained in the following.

The drive wheel 3 comprises a first wheel member 5 and a second wheel member 7. The firstwheel member 5 comprises a shaft interface 14 for the connection to a drive shaft. The driveshaft may thus be connected to the propulsion motor 4 indicated in Fig. 1, for example via atransmission. The drive wheel 3 is configured to rotate around a rotation axis ax during operation of the lawnmower 1. The rotation axis ax is also indicated in Fig. 1.

Below, simultaneous reference is made to Fig. 1 and Fig. 7. The second wheel member 7comprises a ground engaging surface 7' configured to abut against a ground surface 22during operation of the lawnmower 1. ln Fig. 7, the ground engaging surface 7' is onlyschematically illustrated. The ground engaging surface 7' of the drive wheel 3 may be provided at a ring attached to the outer circumference of the second wheel member 7.

The drive wheel 3 comprises a number of grip enhancing members 8. The grip enhancingmembers 8 are movably arranged relative to the ground engaging surface 7' between aretracted and an extracted position. ln Fig. 7, the grip enhancing members 8 are illustrated inthe retracted position. ln embodiments in which the ground engaging surface 7' of the drive wheel 3 is provided at a ring attached to the outer circumference of the second wheel 27 member 7, the outer ring may be provided with thorough holes for the grip enhancingmembers 8. The drive wheel 3 further comprises a mechanism 9 configured to move the gripenhancing members 8 between the retracted position and the extracted position based on a torque betvveen the first and second wheel members 5, 7, as is further explained herein.

According to the embodiments illustrated in Fig. 7, the mechanism 9 comprises a plurality ofarms 25 arranged betvveen the first and second wheel members 5, 7. At least a number ofthe plurality of arms 25 are configured to move when the first wheel member 5 rotatesrelative to the second wheel member 7. ln Fig. 7, the first wheel member 5 is illustrated in afirst position relative to the second wheel member 7 in which the mechanism 9 is configuredto position the grip enhancing members 8 in the retracted position. The mechanism 9 isconfigured to bias the first wheel member 5 towards the first position. Accordingly, the firstwheel member 5 will assume the first position relative to the second wheel member 7 when there is no torque between the first and second wheel members 5, 7.

Fig. 8 illustrates the drive wheel 3 illustrated in Fig. 7 with the first wheel member 5 rotated toa second position. That is, in relation to the drive wheel 3 illustrated in Fig. 7, the first wheelmember 5 has been rotated counterclockwise from the first position to a second position. Ascan be seen in Fig. 8, the mechanism 9 has moved the grip enhancing members 8 in radialdirections R of the drive wheel 3 to the extracted position as a result of the rotation of the firstwheel member 5 to the second position. ln more detail, the mechanism 9 comprises a set ofactuating members 27 which are moved in the radial directions R of the drive wheel 3 uponrotation of the first wheel member 5 from the first position. The grip enhancing members 8are attached to the actuating members 27. According to the illustrated embodiments, two gripenhancing members 8 are attached to one actuating member 27. However, according tofurther embodiments, another number of grip enhancing members 8 may be attached to each actuating member 27.

According to the illustrated embodiments, the arms 25 are configured to be subjected toelastic deformation when the first wheel member 5 rotates from the first position illustrated inFig. 7. ln this manner, the arms 25 apply a counter torque acting to displace the first wheelmember 5 towards the first position when the first wheel member 5 is rotated therefrom.Moreover, due to these features, a mechanism 9 is provided causing movement of the gripenhancing members 8 between the retracted and the extracted position based on the torque between the first and second wheel members 5, 7. 28 As understood from Fig. 7 and Fig. 8, the first wheel member 5 can also be rotated clockwisefrom the first position illustrated 7 towards a third position. Such a third position is similar tothe second position illustrated in Fig. 8 with the difference that at least some of the arms 25 are moved in an opposite direction as compared to the arms 25 illustrated in Fig. 8.

According to the illustrated embodiments, the mechanism 9 is a compliant mechanism,meaning that the arms 25 referred to above are provided in one piece of continuous materialand that the arms 25 are configured to bend upon a relative rotation between the first andsecond wheel members 5, 7. According to the illustrated embodiments, joints 25' betvveenthe arms 25 are bent upon rotation of the first wheel member 5 from the first position.However, preferably, the arms 25 are configured to bend to assume a curved shape when the first wheel member 5 rotates from the first position.

The magnitude of the first and second threshold torques, as referred to herein, may beobtained by adapting the number of arms 25, the stiffness of the arms 25, the stiffness of thejoints 25' between the arms 25, the positions of the arms 25, and the length of the arms 25.The arms 25, the joints 25', the actuating members 27, the first wheel member 5, and thesecond wheel member 7 may be provided in a polymeric material. Moreover, according tosome embodiments herein, the arms 25, the joints 25', the actuating members 27, the firstwheel member 5, and the second wheel member 7 may be provided in one piece ofcontinuous material. The grip enhancing members 8 may be provided in a metal material, such as steel.

Below, simultaneous reference is made to Fig. 1 - Fig. 8. As understood from the hereindescribed, the lawnmower 1 illustrated in Fig. 1 may comprise one or more drive wheels 3explained with reference to Fig. 2 - Fig. 6, or one or more drive wheels 3 explained withreference to Fig. 7 or Fig. 8. ln embodiments in which the lawnmower 1 comprises twowheels 3 arranged on either side of the lawnmower 1, the two drive wheels 3 may be of identical design, or identical but mirrored design. ln the above, the relative rotation between first wheel member 5 and the second wheelmember 7 is in some places referred to as a rotation of the first wheel 5 relative to thesecond wheel member 7. However, as understood by a person skilled in the art, this relativerotation between the first wheel member 5 and the second wheel member 7 may also be referred to as a rotation of the second wheel member 7 relative to the first wheel member 5. 29 As indicated above, the lawnmower 1 comprises a control arrangement 21 configured tocontrol operation of the propulsion motor 4. According to the illustrated embodiments, thecontrol arrangement 21 is configured to selectively perform a control operation in which thepropulsion motor 4 is controlled to apply a torque onto the first wheel member 5 causing amovement of the grip enhancing members 8 towards the extracted position. As understoodfrom the above, the control arrangement 21 may cause movement of the grip enhancingmembers 8 towards the extracted position by applying a torque onto the first wheel member exceeding one of the first and second threshold torques.

According to embodiments herein, the control arrangement 21 is configured to determinewhether to perform the control operation based on input data. The control arrangement 21may be configured to receive the input data from a sensor 28 arranged on the lawnmower 1 and/or may be configured to receive the input data from an external communication unit 38.

According to some embodiments, the input data is representative of a current or impendingslope inclination at the location of the lawnmower 1 and/or a current or impending inclinationangle of the lawnmower 1. The sensor 28 arranged on the lawnmower 1 may be configuredto sense a current inclination angle of the lawnmower1 relative to a horizontal plane hp atthe location of the lawnmower 1. The sensor 28 may be configured to sense the orientationof the lawnmower 1 relative the gravitational field at the location of the lawnmower 1.

According to such embodiments, the sensor 28 may comprise an accelerometer.

As an alternative, or in addition, the sensor 28 may be configured to sense angulardisplacements of the lawnmower 1. According to such embodiments, the sensor 28 maycomprise a gyroscope. Moreover, the control arrangement 21 may be arranged to obtainreference values at one or more predetermined locations, such as at a charging dock.According to such embodiments, the sensor 28 may obtain the current inclination angle bymonitoring changes in inclination angle, for example by sensing changes in inclination angleof the lawnmower 1 and comparing such changes with one or more reference values.According to still further embodiments, the control arrangement 21 may be configured toobtain a current or impending slope inclination at the location of the lawnmower1 and/or acurrent or impending inclination angle of the lawnmower 1 by receiving such data from anexternal source 38, and/or by comparing the current position of the lawnmower 1 and a mapcomprising data indicative of slope inclination angles at the area. The inclination angle of thelawnmower 1, as referred to herein, may be an inclination angle between the longitudinaldirection ld of the lawnmower 1 and the horizontal plane hp at the location of the lawnmower1.

According to these embodiments, the control arrangement 21 may be configured to performthe control operation if a current or impending slope inclination at the location of thelawnmower 1, and/or a current or impending inclination angle of the lawnmower 1, exceeds athreshold inclination. ln this manner, a lawnmower1 is provided having improved conditions for operating in steep slopes.

As an alternative, or in addition, the input data may be representative of one or more oftraction conditions at the location of the lawnmower 1, weather conditions at the location ofthe lawnmower 1, and humidity at the location of the lawnmower 1. The control arrangement21 may be configured to input such input data from a sensor 28 arranged on the lawnmower1 and/or from an external communication unit 38. The control arrangement 21 may thus usesuch input data when determining whether to perform the control operation. ln this manner, alawnmower 1 is provided having improved conditions for operating under conditions with increased risk of wheel slip.

As a further alternative, or in addition, the input data may be representative of presence ofWheel slip of one or more wheels 3, 6 of the lawnmower 1, i.e. wheel slip of the drive wheels3 and/or of the support wheels 6. As an example, the control arrangement 21 may beconfigured to input such input data by monitoring electrical quantities of one or morepropulsion motors 4 of the lawnmower 1. As an alternative, or in addition, the controlarrangement 21 may be configured to input such input data from a positioning unit of thelawnmower 1, and/or an inclination angle sensor of the lawnmower 1. Thus, according tothese embodiments, the control arrangement 21 may determine whether to perform thecontrol operation based on data representative of presence of wheel slip of one or morewheels 3, 6 of the lawnmower 1. lf the data indicates presence of wheel slip of one or morewheels 3, 6 of the lawnmower 1, the control arrangement 21 may perform the control operation.

However, according to some embodiments herein, the control operation comprises stoppingthe lawnmower 1 before controlling the propulsion motor 4 to apply the torque onto the firstwheel member 5. ln this manner, a lawnmower 1 is provided having further improvedconditions for regaining grip after wheel slip of one or more wheels 3, 6 of the lawnmower 1.This because it is ensured that the ground engaging surface 7' of the second wheel member7 is stationary relative to the ground surface 22 before initiating propulsion. Thereby, a lawnmower 1 is provided having further improved conditions for navigating in areas having a 31 high risk of wheel slip, such as undulated areas. Moreover, the risk of unwanted marks is reduced in the operated area.

One skilled in the art will appreciate the control performed by the control arrangement 21described herein may be implemented by programmed instructions. These programmedinstructions are typically constituted by a computer program, Which, when it is executed inthe control arrangement 21, ensures that the control arrangement 21 carries out the desiredcontrol. The computer program is usually part of a computer program product which comprises a suitable digital storage medium on which the computer program is stored.

The control arrangement 21 may comprise a calculation unit which may take the form ofsubstantially any suitable type of processor circuit or microcomputer, e.g. a circuit for digitalsignal processing (digital signal processor, DSP), a Central Processing Unit (CPU), aprocessing unit, a processing circuit, a processor, an Application Specific Integrated Circuit(ASIC), a microprocessor, or other processing logic that may interpret and executeinstructions. The herein utilised expression “calculation unit” may represent a processingcircuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above.

The control arrangement 21 may further comprise a memory unit, wherein the calculationunit may be connected to the memory unit, which may provide the calculation unit with, forexample, stored program code and/or stored data which the calculation unit may need toenable it to do calculations. The calculation unit may also be adapted to store partial or finalresults of calculations in the memory unit. The memory unit may comprise a physical deviceutilised to store data or programs, i.e., sequences of instructions, on a temporary orpermanent basis. According to some embodiments, the memory unit may compriseintegrated circuits comprising silicon-based transistors. The memory unit may comprise e.g.a memory card, a flash memory, a USB memory, a hard disc, or another similar volatile ornon-volatile storage unit for storing data such as e.g. ROM (Read-Only Memory), PROM(Programmable Read-Only Memory), EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), etc. in different embodiments.

The control arrangement 21 is connected to components of the lawnmower 1 for receivingand/or sending input and output signals. These input and output signals may comprisewaveforms, pulses, or other attributes which the input signal receiving devices can detect asinformation and which can be converted to signals processable by the control arrangement 21. These signals may then be supplied to the calculation unit. One or more output signal 32 sending devices may be arranged to convert calculation results from the calculation unit tooutput signals for conveying to other parts of the control system and/or the component orcomponents for which the signals are intended. Each of the connections to the respectivecomponents of the lawnmower 1 for receiving and sending input and output signals may takethe form of one or more from among a cable, a data bus, e.g. a CAN (controller area network) bus, or some other bus configuration, or a wireless connection. ln the embodiments illustrated, the lawnmower 1 comprises a control arrangement 21 butmight alternatively be implemented wholly or partly in two or more control arrangements or two or more control units.

The computer program product may be provided for instance in the form of a data carriercarrying computer program code for performing the desired control when being loaded intoone or more calculation units of the control arrangement 21. The data carrier may be, e.g. aCD ROM disc, or a ROM (read-only memory), a PROM (programable read-only memory), anEPROM (erasable PROM), a flash memory, an EEPROM (electrically erasable PROM), ahard disc, a memory stick, an optical storage device, a magnetic storage device or any otherappropriate medium such as a disk or tape that may hold machine readable data in a non-transitory manner. The computer program product may furthermore be provided as computerprogram code on a server and may be downloaded to the control arrangement 21 remotely,e.g., over an lnternet or an intranet connection, or via other wired or wireless communication systems.

The control arrangement 21 may be configured to control propulsion of the lawnmower 1,and steer the lawnmower 1, so as to navigate the lawnmower 1 in an area to be operated.The lawnmower 1 may further comprise one or more sensors arranged to sense a magneticfield of a wire, and/or one or more positioning units, and/or one or more sensors arranged todetect an impending or ongoing collision event with an object. The one or more positioningunits may comprise a space based satellite navigation system such as a Global PositioningSystem (GPS), The Russian GLObal NAvigation Satellite System (GLONASS), EuropeanUnion Galileo positioning system, Chinese Compass navigation system, or lndian RegionalNavigational Satellite System. As an alternative, or in addition, the control arrangement 21may be configured to obtain data from, or may comprise, one or more positioning unitsutilizing a local reference source, such as a local sender and/or a wire, to estimate or verify a current position of the lawnmower 1. 33 ln addition, the lawnmower 1 may comprise a communication unit connected to the controlarrangement 21. The communication unit may be configured to communicate With a remotecommunication unit 38 to receive instructions therefrom and/or to send information thereto.The communication may be performed wirelessly over a wireless connection such as theinternet, or a wireless local area network (WLAN), or a Wireless connection for exchangingdata over short distances using short-wavelength, i.e. ultra-high frequency (UHF) radio waves in the industrial, scientific, and medical (ISM) band from 2.4 to 2.485 GHz.

The control arrangement 21 may be configured to control propulsion of the lawnmower 1,and steer the lawnmower 1, so as to navigate the lawnmower 1 in a systematic and/orrandom pattern to ensure that an area is completely covered, using input from one or more ofthe above described sensors and/or units. Furthermore, the lawnmower 1 may comprise oneor more batteries arranged to supply electricity to components of the lawnmower 1. As anexample, the one or more batteries may be arranged to supply electricity to propulsionmotors 4 of the lawnmower 1 by an amount controlled by the control arrangement 21.Moreover, the one or more batteries may be arranged to supply electricity a motor configured to power the cutting unit 10. lt is to be understood that the foregoing is illustrative of various example embodiments andthat the invention is defined only by the appended claims. A person skilled in the art willrealize that the example embodiments may be modified, and that different features of theexample embodiments may be combined to create embodiments other than those describedherein, without departing from the scope of the present invention, as defined by the appended claims.

As used herein, the term "comprising" or "comprises" is open-ended, and includes one ormore stated features, elements, steps, components, or functions but does not preclude thepresence or addition of one or more other features, elements, steps, components, functions, or groups thereof.

Claims

1. A lawnmower (1) comprising: - at least one drive wheel (3), and - a propulsion motor (4) configured to rotate the drive wheel (3), wherein the drive wheel (3) comprises: - a first wheel member (5) connected to the propulsion motor (4), and - a second wheel member (7) comprising a ground engaging surface (7') configured toabut against a ground surface (22) during operation of the lawnmower (1), characterized in that the drive wheel (3) comprises: - a number of grip enhancing members (8) movably arranged relative to the groundengaging surface (7') bet\Neen a retracted and an extracted position, and - a mechanism (9) configured to move the grip enhancing members (8) between theretracted and the extracted position based on a torque between the first and secondwheel members (5, 7),wherein the mechanism (9) is configured to move the grip enhancing members (8) to the extracted position when a torque between the first and second wheel members (5, 7) having a first torque direction (Td1) rises above a first threshold torque and is configured to move the grip enhancing members (8) to the extracted position when a torque between the first and second wheel members (5, 7) having a second torque direction (Td2) rises above a second threshold torque, wherein the second torque direction (Td2) is opposite to the first torque direction (Td1). The lawnmower (1) according to claim 1, wherein the first wheel member (5) isconfigured to rotate relative to the second wheel member (7) between a first and asecond position based on the torque between the first and second wheel members (5,7). The lawnmower (1) according to claim 2, wherein the mechanism (9) is configured tomove the grip enhancing members (8) to the retracted position upon rotation of firstwheel member (5) to the first position, and wherein the drive wheel (3) comprises one ormore elastic members (15) configured to bias the first wheel member (5) towards the first position. The lawnmower (1) according to any one of the preceding claims, wherein thelawnmower (1) is accelerated in a forward direction (fd) of the lawnmower (1) when a torque having the first torque direction (Td1) is applied onto the first wheel member (5). The lawnmower (1) according to any one of the preceding claims, wherein thelawnmower (1) is accelerated in a reverse direction (rd) of the lawnmower (1 ) when a torque having the second torque direction (Td2) is applied onto the first wheel member (5). The lawnmower (1) according to any one of the preceding claims, wherein one of thefirst and second threshold torques is lower than the other of the first and second threshold torques. The lawnmower (1) according to any one of the preceding claims, wherein themechanism (9) comprises a number of cam surfaces (11) and a number of followers (13) each abutting against a cam surface (1 1) of the number of cam surfaces (11). The lawnmower (1) according c|aim 7, wherein the first wheel member (5) comprises the cam surfaces (11). The lawnmower (1) according to c|aim 7 or 8, wherein the mechanism (9) comprises a number of elastic members (15) forcing the followers (13) against the cam surfaces (11). The lawnmower (1) according to any one of the c|aims 7 - 9, wherein the cam surfaces(11) are curve-shaped in a plane (P) perpendicular to a rotation axis (ax) of the drivewheel (3). The lawnmower (1) according to any one of the c|aims 7 - 10, wherein the drive wheel (3) comprises the same number of cam surfaces (11) as the number of followers (13). The lawnmower (1) according to any one of the c|aims 7 - 11, wherein a follower (13) ofthe number of followers (13) is configured to assume a position between two adjacentcam surfaces (1 1) when the torque between the first and second wheel members (5, 7) is below a threshold torque. The lawnmower (1) according to any one of the c|aims 1 - 6, wherein the mechanism (9)comprises a plurality of arms (25) arranged between the first and second wheelmembers (5, 7), and wherein at least a number of the plurality of arms (25) areconfigured to move based on the torque between the first and second wheel members(5, 7) so as to cause the movement of the grip enhancing members (8) between the retracted and the extracted position. The lawnmower (1) according to claim 13, Wherein at least a number of the plurality ofarms (25) are configured to be subjected to elastic deformation when the torque between the first and second wheel members (5, 7) rises above a threshold torque. The lawnmower (1) according to any one of the claims 1 - 6, or claim 13 or 14, Wherein the mechanism (9) is a compliant mechanism. The lawnmower (1) according to any one of the preceding claims, Wherein the lawnmower (1) is a self-propelled robotic lawnmower (1). The lawnmower (1) according to any one of the preceding claims, Wherein thelawnmower (1) comprises a control arrangement (21) configured to control operation ofthe propulsion motor (4), and Wherein the control arrangement (21) is configured toselectively perform a control operation in which the propulsion motor (4) is controlled toapply a torque onto the first wheel member (5) causing a movement of the grip enhancing members (8) towards the extracted position. The lawnmower (1) according to claim 17, Wherein the control arrangement (21) isconfigured to determine whether to perform the control operation based on input data,Wherein the input data is representative of one or more of a current or impending slopeinclination at the location of the lawnmower (1), a current or impending inclination angleof the lawnmower (1), traction conditions at the location of the lawnmower (1 ), weatherconditions at the location of the lawnmower (1), humidity at the location of thelawnmower (1 ), and presence of wheel s|ip of one or more wheels (3, 6) of the lawnmower (1 ). The lawnmower (1) according to claim 17 or 18, Wherein the control operation comprisesstopping the lawnmower (1) before controlling the propulsion motor (4) to apply the torque onto the first wheel member (5). A drive wheel (3) for a lawnmower (1), Wherein the lawnmower (1) comprises apropulsion motor (4) configured to rotate the drive Wheel (3), and Wherein the drive wheel (3) comprises: - a first wheel member (5) configured to be connected to the propulsion motor (4) of the lawnmower (1 ), 4 - a second wheel member (7) comprising a ground engaging surface (7') configured toabut against a ground surface (22) during operation of the lawnmower (1),- a number of grip enhancing members (8) movably arranged relative to the groundengaging surface (7') bet\Neen a retracted and an extracted position, and- a mechanism (9) configured to move the grip enhancing members (8) between theretracted and the extracted position based on a torque between the first and secondwheel members (5, 7),wherein the mechanism (9) is configured to move the grip enhancing members (8) tothe extracted position when a torque between the first and second wheel members (5, 7)having a first torque direction (Td1) rises above a first threshold torque, characterized inthat the mechanism (9) is configured to move the grip enhancing members (8) to theextracted position when a torque between the first and second wheel members (5, 7)having a second torque direction (Td2) rises above a second threshold torque, wherein the second torque direction (Td2) is opposite to the first torque direction (Td1).