SE2250723A1

SE2250723A1 - Wheel kit for a lawn mower support wheel arrangement

Info

Publication number: SE2250723A1
Application number: SE2250723A
Authority: SE
Inventors: Johan Bengtzohn; Robert Blom
Original assignee: Husqvarna Ab
Priority date: 2022-06-16
Filing date: 2022-06-16
Publication date: 2023-12-17

Abstract

The present invention relates to a wheel kit (300) for a lawn mower support wheel arrangement. The invention further relates to a lawn mower support wheel arrangement (190) comprising a caster wheel (120, 130) and a caster arm (195), wherein the caster wheel forms a support wheel of the lawn mower and comprises the wheel kit according to the invention. The invention also relates to a robotic lawn mower (100), comprising the wheel kit and/or the lawn mower support wheel arrangement. The wheel kit comprises a wheel front portion (301) and a wheel shield (303). The wheel front portion is adapted to form a side of the caster wheel facing the caster arm. The wheel front portion is further configured to be rotatable around a wheel axle (221a) of the caster wheel. The wheel shield has an opening (307) for the wheel axle and is configured to be stationary in relation to the wheel axle. A diameter (d1) of the wheel shield is at least 50% of a diameter (d2) of the wheel front portion

Description

WHEEL KIT FOR A LAWN MIOWER SUPPORT WHEEL ARRANGEMENT TECHNICAL FIELD The present invention relates to a wheel kit for a lawn mower support wheel arrangement. The invention further relates to a lawn mower support wheel arrangement comprising a caster wheel and a caster arm, wherein the caster wheel comprises the wheel kit according to the invention. The invention also relates to a robotic lawn mower, comprising the wheel kit and/or the lawn mower support wheel arrangement.

BACKGROUND A robotic lawn mower is a lawn mower capable of cutting grass in areas in an autonomous manner, i.e. without the intervention or direct control of a user. The robotic lawn mower is typically self-propelled. Some robotic lawn mowers require a boundary wire around a lawn that defines the area to be mowed. Such robotic lawn mowers use a sensor to locate the wire and thereby the boundary of the area to be trimmed. As an alternative, or in addition, robotic lawn mowers may comprise other types of positioning units and sensors, e.g. sensors for detecting an event, such as a co||ision with an object within the area. The robotic lawn mower may move in a systematic and/or random pattern to ensure that the area is completely cut. The robotic lawn mower is e.g. used to cut grass in areas used for aesthetic and recreational purposes, such as gardens, parks, city parks, sports fields, lawns around houses, apartments, commercial buildings, offices, and the like. A robotic lawn mower usually comprises one or more batteries and one or more electrically driven cutting units powered by the one or more batteries. ln some cases, the robotic lawn mower uses the wire to locate a recharging dock used to recharge the one or more batteries.

Further, a robotic lawn mower typically comprises two or more drive wheels, configured to propel the robotic lawn mower during operation thereof, and one or more support wheels, configured to support the robotic lawn mower during operation thereof. The one or more support wheels are commonly of the type known as caster wheels, which are rotatably attached to a lawn mower body of the robotic lawn mower by means of a swivel joint. The caster wheel is further rotatable around a wheel axle normally being substantially parallel to the ground assuming the ground is flat.

When the robotic lawn mower moves around, it may happen that a grass blade gets twisted around the wheel axle, or even rolled up around the wheel axle. After a while, there may thus be a build-up of grass blades around the wheel axle. This may cause energy loss and/or other mechanical problems. The grass blades may also make the support wheel look dirty. To this end, for prior art robotic lawn mowers, a manual cleaning of the twisted and/or rolled-up grass blades may be desirable.

Furthermore, cut grass may stick to the side of the support wheel, which may make the support wheel look dirty and may potentially influence the mechanics of the support wheel. Hence, a manual cleaning of the side of the support wheel may also in that case be desirable for prior art robotic lawn mowers.

The users of robotic lawn mowers generally prefer that their robotic lawn mower has a neat and tidy visual appearance. Since robotic lawn mowers work autonomously, they usually do not get any frequent inspection and potential cleaning. lt is thus desirable to keep the need for cleaning as low as possible. lt is generally desirable that the lawn mower support wheel arrangement is durable and simple to service. lt may also be desirable that the components are replaceable separate from each other, such that the lawn mower support wheel arrangement does not have to be replaced as a whole because only a single component or a few components are broken down or worn out. lt is further desirable to keep the need for maintenance and service as low as possible.

Furthermore, generally, on today's consumer market, it is an advantage if products, such as robotic lawn mowers and associated components, systems, and arrangements, such as the lawn mower support wheel arrangement, have conditions and/or characteristics suit- able for being manufactured and assembled in a cost-efficient manner.

SUMMARY ln view of the above, an object of the invention is to provide a wheel kit for a lawn mower support wheel arrangement according to claim 1, a lawn mower support wheel arrange- ment according to claim 11 and/or a robotic lawn mower according to claim 14, which alleviates at least one of the drawbacks of the prior art, or which at least provides a suitable alternative. Variations of the invention are set out in the dependent claims and in the following description.

The wheel kit according to the invention is intended to form part of a lawn mower support wheel arrangement, which comprises a caster wheel, intended to form a support wheel of the lawn mower, and a caster arm. The wheel kit comprises a wheel front portion and a wheel shield. The wheel front portion is adapted to form a side of the caster wheel facing the caster arm. The wheel front portion is further configured to be rotatable around a wheel axle for the caster wheel. The wheel shield has an opening for the Wheel axle and is con- figured to be stationary in relation to the Wheel axle and, hence, also stationary in relation to the wheel front portion. A diameter of the wheel shield is at least 50% of a diameter of the wheel front portion. The wheel shield is typically disc-shaped.

The wheel kit according to the invention may be retrofitted into an existing support wheel by replacing the corresponding components. The other components of the lawn mower support wheel arrangement may be the same as for a prior art lawn mower support wheel arrangement, e.g. the one described herein. Accordingly, the wheel kit according to the invention may be used in a prior art lawn mower support wheel arrangement if exchanging the wheel shield and the wheel front portion. Hence, the wheel kit according to the invention may be sold as a spare part.

Due to the configuration of the wheel shield of the wheel kit according to the invention, the risk that a grass blade is twisted around the wheel axle, such that the grass blade even- tually is rolled up around the wheel axle is reduced or even avoided. Hence, there is less risk for a build-up of grass blades around the wheel axle, which could cause energy loss and/or other mechanical problems. This will also make the support wheel look tidier than a prior art support wheel would have looked.

Depending on the height of the grass to be mowed, a part of the wheel shield will be inserted into the grass of the lawn, such that the grass can help to keep this part clean by brushing it. This contributes to a tidier look of the support wheel.

The lawn mower support wheel arrangement with the wheel kit according to the invention is durable and simple to service. The wheel shield and the wheel front portion of the wheel kit according to the invention are replaceable separate from each other and separate from the rest of the support wheel, such that the lawn mower support wheel arrangement does not have to be replaced as a whole because only a single component or a few components are broken down or worn out.

The wheel kit according to the invention and the lawn mower support wheel arrangement according to the invention will help keeping the need for maintenance and service as low as possible. lt can be manufactured and assembled in a cost-efficient manner.

The wheel front portion and the wheel shield may comprise, or consist of, polymeric materials, such as PP, polypropylene, or PA, polyamide. These materials are relatively cheap. Further, any retaining means, such as a snap-in connection, can easily be provided in a component comprising such a material.

As an alternative or a complement, the wheel front portion and the wheel shield may comprise, or consist of, of a metallic material or an alloy. The metallic material or alloy may be used to provide a desired weight distribution for the robotic lawn mower.

The diameter of the wheel shield may be at least 60% of the diameter of the wheel front portion, preferably at least 70%, more preferably at least 75%, most preferably at least 80% of the diameter of the wheel front portion. The diameter may also be at least 85% or at least 90% of the diameter of the wheel front portion.

Hence, the diameter of the wheel shield may be at least 6 cm, preferably at least 7 cm, more preferably at least 8 cm.

The diameter of the wheel shield may be at the most 98% of the diameter of the wheel front portion, preferably at the most 95%, more preferably at the most 90%, most preferably at the most 85% of the diameter of the wheel front portion. Thereby, it can be avoided that the wheel shield, which is stationary in relation to the wheel axle, comes in contact with the ground. This helps to reduce wear of the wind shield. Hence, the wheel front portion, which rotates with the support wheel, extends further radially outwards, such that contact with the ground, if any contact, is made with the wheel front portion. However, normally a traction portion of the support wheel has the primary contact to the ground.

Accordingly, the wheel shield may have a diameter being in the range of 50%-98% of the diameter of the wheel front portion, such as in the range of 60%-95% or 70%-90% or 80%- 85% of the diameter of the wheel front portion.

Often the traction portion of the support wheel has an arched cross-profile, such that the traction portion extends further radially outwards than the wheel front portion. ln that case, the diameter of the wheel shield may be at the most 90% of the diameter of the wheel front portion, preferably at the most 85%, more preferably at the most 80%, most preferably at the most 75% of a maximal diameter of the traction portion.

The wheel front portion may comprise a receptacle for receiving the wheel shield. The receptacle should have a diameter being large enough to receive the wheel shield. Further, the receptacle should allow the wheel front portion to rotate in relation to the wheel shield. The receptacle typically has a depth being the same or about the same as the thickness of the wheel shield at its peripheral edge. Preferably, the wheel front portion has a rim portion located radially outwards of the receptacle, which rim portion may form a radially outermost portion of the wheel front portion. The receptacle and the optional rim portion help to protect the wheel shield, especially its peripheral edge, e.g. from wear.

A front surface of the wheel shield adapted to face away from the wheel front portion may have a matt surface structure. Hence any scratch that the wheel shield would be subjected to, e.g. if the support wheel would run into a stone, Will be less visible.

At least a portion of the front surface of the wheel shield, preferably the whole or substan- tially the whole front surface, may bulge outwards, e.g. being convex and/or dome-shaped. As mentioned above, a part of the wheel shield will be inserted into the grass of the lawn, such that the grass can help to keep this part clean by brushing it. lf the front surface of the wheel shield bulges outwards, the grass blades are able to brush the front surfaces at a more efficient angle as compared to as for a flat front surface. Since the wheel shield does not rotate in relation to the ground, it has been found advantageous from a cleaning point of view that it is inclined in relation to the ground.

The front surface of the wheel shield may comprise a groove adapted to receive a part of the caster arm, the groove extending in an extension direction going from a centre of the Wheel shield to the peripheral edge of the wheel shield. When the wheel shield is mounted in the support wheel, this groove will be directed vertically upwards assuming the lawn mower is standing on flat ground. Thereby, it is possible to position at least a portion of this part of the caster arm in the wheel shield. Hence, there will be no interspace between this part of the caster arm and the wheel shield. This is advantageous, since otherwise grass blades may accumulate in this interspace. When this part of the caster arm is located in the groove, the wheel shield together with this part of the caster arm will have a relatively smooth outer surface, which is less prone of becoming dirty by cut grass sticking to it. Further, with such a construction, the grass of the lawn may help to brush also the part of the wheel shield and the wheel front portion otherwise being hidden behind the caster arm.

This contributes to a tidier look of the support wheel.

The front surface of the wheel shield may have a three-dimensional shape, which is curved as seen in a cross-section taken through a centre of the wheel shield in a direction being perpendicular to the extension direction of the groove, i.e. in a horizontal direction assum- ing the lawn mower is standing on flat ground, and/or which three-dimensional shape is flat along the groove as seen in the extension direction of the groove, i.e. in a vertical direction assuming the lawn mower is standing on flat ground. Such a three-dimensional shape has been found advantageous in order to avoid grass sticking to the side of the support wheel, since the grass of the lawn will help to keep the support wheel clean.

The groove may comprise retaining means configured to retain the part of the caster arm in the groove. The retaining means thus helps to ascertain that the part of the caster arm stays in the groove when the lawn mower is in operation. The retaining means are prefer- ably resilient, such as snap-in means. Thereby, it is easy to attach the part of the caster arm in the groove to the wheel shield and also to loosen it and reattach it if desired.

The present invention also relates to a lawn mower support wheel arrangement comprising a caster wheel and a caster arm. A first end portion of the caster arm is configured to be rotatably attached to a main body of a robotic lawn mower. A second end portion of the caster arm, being opposite to the first end portion, i.e. at the opposite end of the caster arm, forms a wheel axle for the caster wheel. The caster wheel forms a support wheel of the lawn mower and comprises the wheel kit according to the invention, wherein the wheel front portion of the wheel kit and the wheel shield face in the direction of the caster arm. The caster wheel further comprises a wheel outside portion, facing away from the caster arm, and a circumferential traction portion, provided with traction means, such as a traction pattern and/or a tyre attached to, or integrated with at least one of the wheel front portion and the wheel outside portion. The wheel front portion, the wheel outside portion and the traction portion are configured to rotate around the wheel axle, while the wheel shield of the wheel kit is stationary in relation to the wheel axle.

The traction portion is provided with, comprises or consists of traction means, such as a traction pattern and/or a tyre, e.g. a rubber tyre. The traction portion is in contact with the ground. The traction means helps to minimize, or preferably to avoid, the risk of the support wheel slipping in relation to the ground. The traction portion may be attached to the wheel outside portion and/or to the wheel front portion.

The caster arm may comprise the first end portion, followed by a first knee bending about 90 degrees, followed by a first intermediate portion, followed by a second knee bending about 90 degrees, followed by a second intermediate portion, the second intermediate portion being parallel to the first end portion, followed by a third knee bending about 90 degrees, followed by the second end portion, the second end portion being parallel to the first intermediate portion, optionally with further intermediate portions and/or further knees. Such a caster arm provides a vertical arm portion, i.e. the first end portion, suitable for rotatable attachment to the main body of a robotic lawn mower and a horizontal arm portion, i.e. the second end portion, suitable for use as a wheel axle for the support wheel. The knees make it possible to locate the attachment to the main body over the support wheel, at the same time as the caster arm does not interfere with the support wheel, such that the support wheel can rotate freely in relation to the caster arm.

The lawn mower support wheel arrangement may comprise a wheel kit including the groove described herein, wherein the groove is adapted to receive at least a part of the second intermediate portion of the caster arm. The groove has a depth as seen in the direction of the wheel axle. Preferably the depth is larger than a radius of the second intermediate portion of the caster arm, more preferably larger than 1.4 X the radius, more preferably larger than 1.7 X the radius. The groove will be directed vertically upwards assuming the lawn mower is standing on flat ground. Thereby, it is possible to position at least a part of the second intermediate portion of the caster arm in the wheel shield. Hence, there will be no interspace between this part of the caster arm and the wheel shield. This is advantageous, since othenNise grass blades may accumulate in this interspace. The wheel shield together with this part of the caster arm will have a relatively smooth outer surface, which is less prone of becoming dirty by grass sticking to it. Further, with such a construc- tion, the grass of the lawn may help to brush also the part of the wheel shield and the wheel front portion othenNise being hidden behind the caster arm. This contributes to a tidier look of the support wheel.

The present invention further relates to a robotic lawn mower, comprising a wheel kit according to the invention and/or a lawn mower support wheel arrangement according to the invention. The robotic lawn mower preferably comprises one or two lawn mower support wheel arrangements according to the invention. The robotic lawn mower is typically self-propelled. lt is capable of cutting grass in areas in an autonomous manner, i.e. without the intervention or direct control of a user.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will hereinafter be further explained by means of non-limiting examples with reference to the appended drawings wherein: Fig. 1 shows a robotic lawn mower according to the invention, which comprises a lawn mower support wheel arrangement according to the invention. Fig. 2 shows a schematic overview of an exemplary work area. Fig. 3 shows part of a robotic lawn mower with a lawn mower support wheel arrangement according to prior art.

Fig. 4 shows an exploded view of the lawn mower support wheel arrangement of Fig. 3. Fig. 5 shows a lawn mower support wheel arrangement according to the invention. Fig. 6 shows a caster arm of the lawn mower support wheel arrangement of Fig. 5. Fig. 7 shows a support wheel of the lawn mower support wheel arrangement of Fig. 5. Fig. 8 shows some of the components of the support wheel of Fig. 7 in an exploded view. Fig. 9 shows a support wheel of another lawn mower support wheel arrangement according to the invention.

Fig. 10 shows some of the components of the support wheel of Fig. 9 in an exploded view. lt should be noted that the appended drawings are not necessarily drawn to scale and that the dimensions of some features of the present invention may have been exaggerated for the sake of clarity.

DETAILED DESCRIPTION The invention will in the following be exemplified by embodiments. lt should however be realized that the embodiments are included in order to explain principles of the invention and not to limit the scope of the invention, defined by the appended claims. Details from two or more of the embodiments may be combined with each other.

Figure 1 schematically illustrates a robotic lawn mower 100 according to the invention. Figure 2 shows a schematic overview of an exemplary work area 201, e.g. a garden, in which the robotic lawn mower 100 may be set to operate.

The work area 201 is delimited by a boundary. ln the illustrated embodiment, the work area 201 is enclosed by a boundary wire 203 with the purpose of keeping the robotic lawn mower 100 inside the work area 201. An electric control signal may be transmitted through the boundary wire 203, thereby generating an electromagnetic field emanating from the boundary wire 203. The robotic lawn mower 100 is in that case typically arranged with one or more control signal sensors (not shown) adapted to sense the control signal. The work area 201 is typically arranged, such that the robotic lawn mower 100 can dock with a charging station 205.

Alternatively, or as a complement, the work area 201 may be delimited by a virtual boundary, e.g. provided by a map application or stored coordinates in the robotic lawn mower 100. Hence, the robotic lawn mower 100 may, as an option, comprise a navigation system that is adapted for satellite navigation by means of GPS, i.e. Global Positioning System, or some other GNSS system, i.e. Global Navigation Satellite System, for example using RTK, i.e. Real Time Kinematic. ln addition to this, or as an alternative, the navigation system can be adapted for navigation by means of a local base station that for example can be housed in the charging station 205 and provide a navigation signal that further increases the navigation accuracy.

The robotic lawn mower100 comprises a main body 110 and a plurality of wheels. ln the illustrated embodiment, the robotic lawn mower 100 has four wheels, two front wheels and two rear wheels, whereof the two front wheels 120, 130 and one of the rear wheels 140 are visible in the illustrated perspective of Fig. 1. The rear wheels 140 are drive wheels, which are used to propel the robotic lawn mower 100. The front wheels 120, 130 are support wheels, which support the main body 110 by abutting against a ground surface.

The robotic lawn mower 100 comprises a grass cutting device 150, such as a rotating blade or a disc with a plurality of separate cutting members, e.g. rotating blades, driven by a cutter motor. The energy of each cutting member typically is below 2 Joule when cutting. The weight of each cutting member is typically in the ranges of 1-5 grams, such as e.g. 3.4 grams. Thickness is typically the range of 0.5-1.0 mm, such as e.g. 0.63 mm.

The robotic lawn mower 100 comprises at least one rechargeable electric power source 160 for providing power to the drive wheels 140 and/or to the cutter motor. The recharge- able electric power source 160 is arranged to be charged by means of received charging current from the charging station 205, received through charging skids 170 or other suit- able charging connectors. lnductive charging without galvanic contact, only by means of electric contact, is also conceivable. The rechargeable electric power source 160 may comprise one or more batteries that can be separately arranged or be arranged in an integrated manner to form a combined battery.

The robotic lawn mower 100 may, as an option, comprise at least one environmental detection sensor 180, e.g. an imaging sensor such as a camera device, which is adapted to provide images of the environment around the robotic lawn mower 100. Other examples of commonly used environmental detection sensors in robotic lawn mowers are a radar sensor, an IR sensor, an ultrasonic sensor and/or a Lidar sensor. The one or more environ- mental detection sensors 180 are helpful when the robotic lawn mower 100 moves around in order to help its navigation ability.

Figure 3 shows parts of a prior art robotic lawn mower seen obliquely from below, such that an underside of part of the main body 207 is seen, showing details of the grass cutting device 209. One of the rear wheels 211, used for driving of the robotic lawn mower, is partly hidden by the grass cutting device 209. Adjacent to a front of the robotic lawn mower, one of the support wheels 213 is seen. The support wheel 213 is in the form of a caster wheel and forms part of a lawn mower support wheel arrangement 215 according to prior art.

The components of the prior art lawn mower support wheel arrangement 215, including the support wheel 213 and a caster arm 217, are shown in Figure 4 in an exploded view. The caster arm 217 is rotatably attached to the main body 207, indicated by dashed lines, around a swivel joint, e.g. as described in WO 2021/228633. 11 The caster arm 217 comprises a first end portion 219 being configured to be rotatably attached to the main body 207. A second end portion 221 of the caster arm 217, being opposite to the first end portion 219, i.e. at the opposite end of the caster arm 217, forms a wheel axle for the support wheel 213. The caster arm 217 comprises the first end portion 219, followed by a first knee 223 bending about 90 degrees, followed by a first intermediate portion 225, followed by a second knee 227 bending about 90 degrees, followed by a second intermediate portion 229, the second intermediate portion 229 being parallel to the first end portion 219, followed by a third knee 231 bending about 90 degrees, followed by the second end portion 221, the second end portion 221 being parallel to the first intermedi- ate portion 225. There may optionally be further intermediate portions and/or further knees.

A bearing assembly 233 is located around the first end portion 219 of the caster arm 217 and provides the rotatable attachment of the lawn mower support wheel arrangement 215 to the main body 207. The bearing assembly 233 comprises a first and a second ball bearing 235, 237, but other types of bearings known to the skilled person may also be used. The illustrated bearing assembly 233 also comprises, as seen from an upper end 239 of the first end portion 219: a lock washer 241, a first washer 243, a second washer 245, a third washer 247. The number and types of washers may vary. The first end portion 219 forms a spindle for the bearing assembly 233.

The support wheel 213 comprises a shield kit 249 comprising a prior art wheel shield 251 and an inner shield component 253. The support wheel 213 further comprises a first sealing 255, a first ball bearing 257, a prior art wheel front portion 259, a traction portion 261, a second sealing 263, a second ball bearing 265, a washer 267, a lock washer 269, a wheel outside portion 271 and fastening means 273, illustrated as screws. The first ball bearing 257 and the second ball bearing 265 form a bearing assembly allowing the support wheel 213 to rotate around the second end portion 221 of the caster arm 217, which second end portion 221 forms the wheel axle of the support wheel 213. Alternatively, other kinds of bearings known to the skilled person may be used. Further, the number and types of washers and sealings used in the support wheel 213 may vary.

The wheel shield 251 is stationary in relation to the second end portion 221 of the caster arm 217, i.e. it does not rotate around the second end portion 221 forming the wheel axle of the support wheel 213. 12 The traction portion 261 is provided with, comprises or consists of traction means, such as a traction pattern and/or a tyre, e.g. a rubber tyre as is illustrated. The traction portion 261 is in contact with the ground. The traction means helps to minimize, or preferably to avoid, the risk of slipping in relation to the ground. The traction portion 261 may be attached to the wheel outside portion 271, as is illustrated. Hence, the illustrated wheel outside portion 271 has a receptacle 275 being configured for holding the traction portion 261. ln addition, or as an alternative, the traction portion 261 may be attached to the wheel front portion 259.

The wheel front portion 259, the traction portion 261, the wheel outside portion 271 and the fastening means 273 are rotatable around the second end portion 221 forming the wheel axle of the support wheel 213.

The inner shield component 253, the first sealing 255, the second sealing 263, the washer 267 and the lock washer 269 may, each of them, either be stationary or rotatable in relation to the second end portion 221 of the caster arm 217.

When the prior art robotic lawn mower moves around, it may happen that a grass blade is picked up by the rotating support wheel 213 and reaches the wheel axle, i.e. the second end portion 221 of the caster arm 217. Since the wheel axle is stationary in relation to the support wheel 213 itself, the rotation of the support wheel 213 when the robotic lawn mower 100 moves around may twist the grass blade around the wheel axle, such that the grass blade eventually may be rolled up around the wheel axle. After a while, there may thus be a build-up of grass blades around the wheel axle. This may cause energy loss and/or other mechanical problems. The grass blades may also make the lawn mower support wheel arrangement 215 look dirty. Hence, a manual cleaning of the twisted and rolled-up grass blades may be desirable.

Furthermore, cut grass may stick to the side of the support wheel 213, e.g. to the wheel shield 251 or to the wheel front portion 259, which may as well make the support wheel 213 look dirty and may potentially influence the mechanics of the support wheel 213. Hence, a manual cleaning of the side of the support wheel may in that case be desirable for prior art robotic lawn mowers. This problems tends to be worst on the wheel shield 251 and the wheel front portion 259 being in the direction, in which the grass cutting device 209 throws the cut grass. 13 Figure 5 shows parts of the robotic lawn mower 100 according to the invention of Figure 1 seen obliquely from below, such that an underside of part of the main body 110 is seen, showing details of the grass cutting device 150, i.e. a similar perspective as in Figure 3. One of the rear wheels 145, used for driving of the robotic lawn mower 100, is partly hidden by the grass cutting device 150. Adjacent to a front of the robotic lawn mower 100, one of the support wheels 120 is seen. The support wheel 120 is in the form of a caster wheel and forms part of a lawn mower support wheel arrangement 190 according to the invention. The lawn mower support wheel arrangement 190 further comprises a caster arm 195.

The caster arm 195, see Figure 6, is similar to the caster arm 217 of the prior art lawn mower support wheel arrangement 215 shown in Figures 3 and 4. Hence, also the caster arm 195 of the lawn mower support wheel arrangement 190 according to the invention comprises a first end portion 219a being configured to be rotatably attached to the main body 110 of the robotic lawn mower 100. A second end portion 221a of the caster arm 195, being opposite to the first end portion 219a, i.e. at the opposite end of the caster arm 195, forms a wheel axle for the support wheel 120. The caster arm 195 comprises the first end portion 219a, followed by a first knee 223a bending about 90 degrees, followed by a first intermediate portion 225a, followed by a second knee 227a bending about 90 degrees, followed by a second intermediate portion 229a, the second intermediate portion 229a being parallel to the first end portion 219a, followed by a third knee 231a bending about 90 degrees, followed by the second end portion 221a, the second end portion 221a being parallel to the first intermediate portion 225a. There may optionally be further intermediate portions and/or further knees.

Figure 7 shows the support wheel 120 in an assembled state. Figure 8 is an exploded view showing some components of the support wheel 120, namely a wheel kit 300 according to the invention and a wheel outside portion 305.

The wheel kit 300 comprises a wheel front portion 301 and a wheel shield 303. Figures 7 and 8 also show the wheel outside portion 305, which may be of the same kind as the wheel outside portion 271 of the prior art lawn mower support wheel arrangement 215 shown in Figures 3 and 4. Most other components of the lawn mower support wheel arrangement 190 according to the invention may be the same as described above for the prior art lawn mower support wheel arrangement 215, and will thus not be described again. 14 Accordingly, the wheel kit 300 according to the invention may be used in a prior art lawn mower support wheel arrangement 215, if exchanging the wheel shield 251 and the Wheel front portion 259, thus Upgrading to the lawn mower support wheel arrangement 190 according to the invention. Hence, the wheel kit 300 according to the invention is suitable to be sold as a spare part.

The wheel shield 303 is disc-shaped with an opening 307 for the wheel axle, i.e. the second end portion 221a of the caster arm 195. The wheel shield 303 is configured to be stationary in relation to the wheel axle 221a. The wheel front portion 301 is, on the other hand, configured to be rotatable around the wheel axle 221a. The wheel front portion 301 comprises a receptacle 309 for receiving the wheel shield 303. A diameter d1 of the wheel shield 303 is at least 50% of a diameter d2 of the wheel front portion 301. Accordingly, the wheel kit 300 according to the invention differs from that of prior art, cf. Figures 3 and 4, by the wheel shield 303 being relatively larger as compared to the wheel front portion 301 than for prior art.

The diameter d1 of the wheel shield 303 may be at least 60% of the diameter d2 of the wheel front portion 301, preferably at least 70%, more preferably at least 75%, most preferably at least 80% of the diameter d2 of the wheel front portion 301. This may correspond to the diameter d1 of the wheel shield 303 being at least 6 cm, preferably at least 7 cm, more preferably at least 8 cm.

The diameter d1 of the wheel shield 303 may be at the most 98% of the diameter d2 of the wheel front portion 301, preferably at the most 95%, more preferably at the most 90%, most preferably at the most 85% of the diameter d2 of the wheel front portion 301. Hence, the wheel front portion 303 extends further radially outwards as compared to the wheel shield 303, such that contact With the ground, if any contact, is made with the wheel front portion 301 and not with the wheel shield 303. However, normally the traction portion of the support wheel 120 has the primary contact to the ground as described for the prior art robotic lawn mower, cf. Figures 3 and 4.

Accordingly, the wheel shield 303 may have a diameter d1 being in the range of 50%-98% of the d2 diameter of the wheel front portion 301, such as in the range of 60%-95% or 70%- 90% or 75%-85% of the diameter d2 of the wheel front portion 301.

Often the traction portion of the support wheel 120 has an arched cross-profile, as may be gleaned in Figure 5, showing a similar traction portion as the traction portion 261 depicted for the prior art robotic lawn mower of Figures 3 and 4, such that the traction portion extends further radially outwards than the wheel front portion 301. ln that case, the dia- meter d1 of the wheel shield 303 may be at the most 90% of the diameter d2 of the wheel front portion 301, preferably at the most 85%, more preferably at the most 80%, most preferably at the most 75% of a maximal diameter of the traction portion.

The receptacle 309 of the wheel front portion 301 has a diameter being large enough to receive the wheel shield 303. Further, the receptacle 309 should allow the wheel front portion 301 to rotate in relation to the wheel shield 303. The receptacle 309 has a depth h being about the same as a thickness te of the wheel shield 303 at its peripheral edge 311. Preferably, and as illustrated, the wheel front portion 301 has a rim portion 313 located radially out\Nards of the receptacle 309, which rim portion 313 forms a radially outermost portion of the wheel front portion 301. The receptacle 309 and the optional rim portion 313 help to protect the wheel shield 303 from wear, especially its peripheral edge 311.

A front surface 315 of the wheel shield 303, adapted to face away from the wheel front portion 301, preferably has a matt surface structure. Hence, any scratch that the wheel shield 303 could be subjected to, e.g. if the support wheel 120 would run into a stone, will be less visible.

At least a portion of the front surface 315 of the wheel shield 303, preferably the whole or substantially the whole front surface 315, may bulge outwards, e.g. being convex and/or dome-shaped. Hence, a thickness to of the wheel shield 303 determined at the opening 307 may be larger than the thickness te of the wheel shield 303 at its peripheral edge 311.

The other components of the lawn mower support Wheel arrangement 190 according to the invention may be the same as in the prior art lawn mower support wheel arrangement 215 described in conjunction with Figures 3 and 4 and are thus not described again. The inward-facing side of the Wheel front portion 301 may thus be corresponding to the inward- facing side of the prior art wheel front portion 259, such that it fits with the wheel outside portion 271, the traction portion 261 and the other components of the prior art lawn mower support wheel arrangement 215. 16 Figures 9 and 10 show another wheel kit 400 according to the invention for a lawn mower support wheel arrangement according to the invention. Figure 9 shows an assembled support wheel, while Figure 10 shows an exploded view.

The wheel kit 400 comprises a wheel front portion 401 and a wheel shield 403. The wheel front portion 401 is attached to a wheel outside portion 405, not comprised in the wheel kit 400, but forming part of the support wheel. The wheel kit 400 i.a. differs from that i||ustrated in Figures 5-8 by the three-dimensional shape of the front surface 415 of the wheel shield 403 _ The wheel front portion 401 comprises a receptacle 409 for receiving the wheel shield 403. Preferably, and as i||ustrated, the wheel front portion 401 has a rim portion 413 located radially out\Nards of the receptacle 409, which rim portion 413 forms a radially outermost portion of the wheel front portion 401. The wheel shield 403 has an opening 407 for the wheel axle, being formed by a second end portion 417 of the caster arm, and a front surface 415, facing a second intermediate portion 419 of the caster arm.

The front surface 415 of the wheel shield 403 comprises a groove 421 adapted to receive a part of the second intermediate portion 419 of the caster arm. The groove 421 extends in an extension direction going from a centre of the wheel shield 403 to a peripheral edge 411 of the wheel shield 403. When the wheel shield 403 is mounted in the support wheel, the groove 421 will be directed vertically upwards assuming the robotic lawn mower 100 is standing on flat ground. Thereby, it is possible to position at least a portion of this part of the caster arm in the wheel shield 403, as is shown in Figure 9. Hence, there will be no interspace between this part of the caster arm and the wheel shield 403. This is advan- tageous, since otherwise grass blades may accumulate in this interspace. When this part of the caster arm is located in the groove 421, the wheel shield 403 together with this part of the caster arm will have a relatively smooth outer surface, see Figure 9, which is less prone of becoming dirty by grass sticking to it and/or to be scratched. Further, with such a configuration, the grass of the lawn may help to brush also the part of the wheel shield 403 and the wheel front portion 401 otherwise being hidden behind the caster arm. This contributes to a tidier look of the support wheel.

The groove 421 has a depth tg as seen in the direction of the wheel axle being formed by the second end portion 417 of the caster arm. Preferably the depth tg is larger than a radius 17 rg of the second intermediate portion 419 of the caster arm, more preferably larger than 1.4 x the radius rg of the second intermediate portion 419 of the caster arm, more preferably larger than 1.7 x the radius rg of the second intermediate portion 419 of the caster arm. Typically, the second end portion 417 of the caster arm forming the wheel axle has a radius ra being the same as the radius rg of the second intermediate portion 419.

The front surface 415 of the wheel shield 403 has a three-dimensional shape, which is curved as seen in a cross-section taken through a centre of the wheel shield 403 in a direction being perpendicular to the extension direction of the groove 421, indicated by A-A in Figure 10, i.e. in a horizontal direction assuming the lawn mower is standing on flat ground. Hence, the thickness tA at the peripheral edge 411 of the wheel shield 403 at the A-A line is rather thin, e.g. a few millimetres, while the thickness tg at the centre, i.e. at the opening 407, is larger than the depth tg of the groove 421. Further, the three-dimensional shape of the front surface 415 is flat or substantially flat along the groove 421 as seen in the extension direction B-B of the groove 421, i.e. in a vertical direction assuming the robotic lawn mower 100 is standing on flat ground. Hence, the thickness tB at the peripheral edge 411 of the wheel shield 403 next to the B-B line is the same or substantially the same as the thickness to at the centre. Such a three-dimensional shape of the front surface 415 has been found advantageous in order to avoid grass sticking to the front surface 415 or to the caster arm, e.g. its second portion 419, since the grass of the lawn will help to keep these clean.

The groove 421 comprises retaining means 423, 425 configured to retain the part of the second intermediate portion 419 in the groove 421. The retaining means 423, 425 thus help to ascertain that the part of the second intermediate portion 419 stays in the groove 421 when the robotic lawn mower is in operation. The retaining means 423, 425 are prefer- ably resilient, such as snap-in means. Thereby, it is easy to attach the part of the second intermediate portion 419 in the groove 421 and hence to the Wheel shield 403, and also easy to loosen it and reattach it if desired.

Further modifications of the invention within the scope of the appended claims are feasible. As such, the present invention should not be considered as limited by the embodiments and figures described herein. Rather, the full scope of the invention should be determined by the appended claims, with reference to the description and drawings.

Claims

Claims A wheel kit (300, 400) for a lawn mower support wheel arrangement (190), which lawn mower support wheel arrangement (190) comprises a caster wheel (120) and a caster arm (195), the wheel kit (300, 400) comprising: - a wheel front portion (301, 401), being adapted to form a side of the caster wheel (120) facing the caster arm (195), the wheel front portion (301, 401) being configured to be rotatable around a wheel axle (221a, 417) for the caster wheel (195), and - a wheel shield (303, 403), having an opening (307, 407) for the wheel axle (221a, 417) and being configured to be stationary in relation to the wheel axle (221a, 417), characterized in that a diameter (d1) of the wheel shield (303, 403) is at least 50% of a diameter (d2) of the wheel front portion (301, 401). The wheel kit (300, 400) according to claim 1, wherein the diameter (d1) of the wheel shield (303, 403) is at least 60% of the diameter (d2) of the wheel front portion (301, 401), preferably at least 70%, more preferably at least 75%, most preferably at least 80% of the diameter (d2) of the wheel front portion (301, 401 ). The wheel kit (300, 400) according to claim 1 or 2, wherein the diameter (d1) of the wheel shield (303, 403) is at least 6 cm, preferably at least 7 cm, more preferably at least 8 cm. The wheel kit (300, 400) according to any one of the preceding claims, wherein the diameter (d1) of the wheel shield (303, 403) is at the most 98% of the diameter (d2) of the wheel front portion (301, 401), preferably at the most 95%, more preferably at the most 90%, most preferably at the most 85% of the diameter (d2) of the wheel front portion (301, 401). The wheel kit (300, 400) according to any one of the preceding claims, wherein the wheel front portion (301, 401) comprises a receptacle (309, 409) for receiving the wheel shield (303, 403).The wheel kit (300, 400) according to any one of the preceding claims, wherein a front surface (315, 415) of the wheel shield (303, 403), adapted to face away from the wheel front portion (301, 401), has a matt surface structure. The wheel kit (300, 400) according to any one of the preceding claims, wherein at least a portion of the front surface (315, 415) of the wheel shield (303, 403), preferably the whole or substantially the whole front surface (315, 415), bulges outwards, e.g. is convex and/or dome-shaped. The wheel kit (400) according to any one of the preceding claims, wherein the front surface (415) of the wheel shield (403) comprises a groove (421) adapted to receive a part of the caster arm (195), the groove (421) extending in an extension direction (B-B) going from a centre of the wheel shield (403) to a peripheral edge (411) of the wheel shield (403). The wheel kit (400) according to claim 8, wherein the front surface (415) of the wheel shield (403) has a three-dimensional shape, which is curved as seen in a cross-section (A-A) taken through a centre of the wheel shield (403) in a direction being perpendicular to the extension direction (B-B) of the groove (421) and/or which is flat along the groove (421) as seen in the extension direction (B-B) of the groove (421 ). The wheel kit (400) according to claim 8 or 9, wherein the groove (421) comprises retaining means (423, 425) configured to retain the part of the caster arm (195) in the groove (421), the retaining means (423, 425) preferably being resilient, such as snap-in means. A lawn mower support wheel arrangement (190) comprising a caster wheel (120) and a caster arm (195), a first end portion (219a) of the caster arm (195) being configured to be rotatably attached to a main body (110) ofa robotic lawn mower (100), a second end portion (221a) of the caster arm (195), being opposite to the first end portion (219a), forming a wheel axle for the caster wheel (120), the caster wheel (195) comprising the wheel kit (300, 400) according to any one of the preceding claims, wherein the wheel front portion (301, 401) and the wheel shield (303, 403) of the wheel kit (300, 400) face the caster arm (195), the caster wheel (120) further comprising a wheel outside portion (305, 405), facing away from the caster arm (195), and a circumferential traction portion (261), provided with traction means, such as a traction pattern and/or a tyre, attached to, or integrated with at least one of the wheel front portion (301, 401) and the wheel outside portion (305, 405), the wheel front portion (301, 401), the wheel outside portion (305, 405) and the traction portion (261) being configured to rotate around the wheel axle (221a, 417), the wheel shield (303, 403) of the wheel kit (300, 400) being stationary in relation to the wheel axle (221a, 417). The lawn mower support wheel arrangement (190) according to claim 11, wherein the caster arm (195) comprises the first end portion (219a), followed by a first knee (223a) bending about 90 degrees, followed by a first intermediate portion (225a), followed by a second knee (227a) bending about 90 degrees, followed by a second intermediate portion (229a, 419), the second intermediate portion (229a, 419) being parallel to the first end portion (219a), followed by a third knee (231a) bending about 90 degrees, followed by the second end portion (221a, 417), the second end portion (221a, 417) being parallel to the first intermediate portion (225a), optionally with further intermediate portions and/or further knees. The lawn mower support wheel arrangement (190) according to claim 11 or 12, when comprising a wheel kit (300, 400) according to any one of claims 8-10, wherein the groove (421) is adapted to receive at least a part of the second intermediate portion (419) of the caster arm (195), the groove (421) having a depth (tg) as seen in the direction of the wheel axle (417), preferably the depth (tg) being larger than a radius (rg) of the second intermediate portion (419) of the caster arm (195), more preferably larger than 1.4 X the radius (rg), more preferably larger than

1.7 x the radius (rg). A robotic lawn mower (100), comprising a wheel kit (300, 400) according to any one of claims 1-10 and/or a lawn mower support wheel arrangement (190) according to any one of claims 11-13, preferably the robotic lawn mower (100) comprising one or two lawn mower support wheel arrangements (190) according to any one of claims 11-13.