Cutting arrangement and lawnmower

Abstract

A cutting arrangement (2) is disclosed comprising a cutting guard (3) and a first and a second cutting unit (11, 12) configured to rotate in opposite rotational directions (r1, r2) such that one or more radially outer portions (11', 12') of the respective first and second cutting units (11) orbits in a respective first and a second circular path (c1, c2) inside the cutting guard (3). The cutting guard (3) further comprises a discharge opening (5) arranged to eject clippings along a main discharge direction (md) from the cutting guard (3). A tangential movement direction (T1, T2) of the first and second cutting units (11, 12) coincides with the main discharge direction (md) at a location within an overlapping area (A) between the first and a second circular paths (c1, c2) upon rotation of the first and second cutting units (11, 12) around the respective first and second rotation axes (ax1, ax2). The present disclosure further relates to a lawnmower (1) comprising a cutting arrangement (2).

Description

[0001] Cutting Arrangement and Lawnmower

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to cutting arrangement configured to be attached to a lawnmower such that a forward direction of the cutting arrangement coincides with a forward direction of the lawnmower. The present disclosure further relates to a lawnmower comprising a cutting arrangement.

[0004] BACKGROUND

[0005] A lawnmower is an apparatus designed to cut the grass of a lawn. Various types of lawnmowers exist on today’s market, including walk-behind mowers and self-propelled robotic lawnmowers. A walk-behind mower usually comprises an elongated handle, allowing a user to push and / or guide the lawnmower. Some walk-behind mowers include a propulsion arrangement configured to drive one or more wheels of the lawnmower, while those lacking a propulsion arrangement are sometimes referred to as “push mowers”. Some lawnmowers comprise a power unit in the form of an electric motor configured to rotate the cutting unit and some lawnmowers comprise a power unit in the form of a combustion engine configured to rotate the cutting unit.

[0006] A self-propelled robotic lawnmower is capable of cutting grass autonomously in various areas. Some robotic lawnmowers require a user to set up a border wire around a lawn that defines the area to be mowed. These lawnmowers use a sensor to locate the wire and thereby the boundary of the mowing area. In addition to the wire, robotic lawnmowers may also comprise other types of positioning units and sensors, for example sensors for detecting an event, such as a collision with an object within the area. The robotic lawnmower may move in a systematic and / or random pattern to ensure that the area is completely cut. A robotic lawnmower usually comprises one or more batteries and one or more electrically driven cutting units being powered by the one or more batteries. In some cases, the robotic lawnmower uses the wire to locate a recharging dock used to recharge the one or more batteries. Generally, robotic lawnmowers operate unattended within the area in which they operate. Examples of such areas are lawns, gardens, parks, sports fields, golf courts and the like.

[0007] Lawnmowers of various types are associated with some mutual problems. One such problem is the energy consumption of the lawnmower. Cutting grass usually requires a significant amount of energy. Due to environmental concerns, it is a great advantage if lawnmowers and associated arrangements and systems can be arranged to operate in an energy-efficient i manner. Moreover, after a certain time of operation, an energy storage unit of a lawnmower, such as a battery or fuel tank, has to be charged or refilled. Thus, by reducing the energy consumption of the lawnmower, more available operational time of the lawnmower can be obtained given a certain energy storing capacity of the energy storage unit of the lawnmower. Furthermore, a more cost-efficient lawnmower can be provided because the consumption of fuel or electricity incurs costs.

[0008] Another problem associated with lawnmowers is the cutting result, which can be subdivided into visual cutting result and uniformity of cutting. The visual cutting result can be defined as the visual cutting result determined by a person viewing a mowed lawn. The uniformity of the cutting can be defined as uniformity of a length of the grass of a mowed lawn, i.e. if straws of the grass in a lawn are cut to a uniform length. Most lawnmowers comprise a cutting arrangement comprising a cutting guard and a cutting unit, wherein the cutting unit is configured to rotate inside the cutting guard during operation.

[0009] A common problem for lawnmowers is that traces may be formed in the lawn having shorter or longer length of grass. Such traces significantly reduce the visual appearance of the lawn. One aspect that reduces the cutting result is that grass tend to bend when a cutting arrangement is moved over the lawn. The grass may then become straighter again which causes an uneven cutting result and impair the visual appearance of the lawn.

[0010] One way to improve the cutting result is to ensure that the grass is lifted towards the cutting unit when cutting unit is moved over the lawn. This can be performed by arranging the cutting unit with one or more surfaces being angled relative to a rotation plane of the cutting unit. In this manner, a negative pressure can be generated inside the cutting guard which lifts grass towards the cutting unit. This method is highly efficient when it comes to cutting result and visual appearance of a lawn after cutting. However, this method is also highly energy consuming. This because the energy needed for creating the negative pressure inside the cutting guard increases the rotational resistance of the cutting unit and hence the energy consumption of the cutting arrangement. Another aspect is that the attack angle of the angled surfaces not only generates a negative pressure inside the cutting guard but also some air flow in unwanted directions which adds to the increase in rotational resistance of the cutting unit and hence the energy consumption of the cutting arrangement.

[0011] Another problem associated with lawnmowers is formation of strings or clumps of clippings on the lawn. Clippings takes time to decompose, and strings or clumps of clippings have a negative impact on the visual cutting result. Moreover, strings or clumps of clippings may disturb and annoy users of the lawn and cause an uneven distribution of nutrients on the lawn, which leads to an uneven subsequent growth of grass in the lawn. Furthermore, strings and clumps of clippings tend to yellow and can smother the grass underneath, leading to decay and rot.

[0012] In some geographical areas, lawns are generally cut at a higher height due to warm climate, cultural habits, and desired visual appearance. Popular choices, such as tall fescue grass, are cold season grasses but are widely used in transition zones for their aesthetic appeal. However, due to its shallow root system, tall fescue grass tends to dry out in hot climates and is sensitive to wheel trampling. Typically, lawns are mowed once a week to a height of 3 - 5 inches, reducing the height by 1 - 2 inches at each mowing. This frequency usually prevents issues with trampled grass.

[0013] Traditionally, rotary mowers with side discharge, including zero-turn and walk-behind models, are common. These mowers have a motor power ranging from 5-30 Hp. The blade design includes bent wings to create a vacuum above 300Pa, lifting the grass before cutting. The contour of the cutting cover around the blades is circular with a tight clearance of 5 - 8mm. To meet standard requirements, the cutting cover's lower vertical edge is situated at least 3 mm below the blades. Usually, high motor power is needed, especially when cutting long clippings; longer clippings require more power. Moreover, these types of cutting arrangements can comprise bent wings of the blades for generating airflow, which consume significant energy.

[0014] Some cutting arrangements comprise several cutting units, such as three cutting units arranged offset laterally and forward in a triangular pattern. Achieving a clean cut between the blades can be challenging, particularly when aiming to save energy and reduce vacuum and airflow. Moreover, it is usually difficult to obtain an efficient evacuation of clippings from such a cutting arrangement. Apart from the risk of formation of strings or clumps of clippings, an efficient evacuation of clippings important to prevent interference with subsequent cutting.

[0015] Moreover, build-up of clipping on inside surfaces of a cutting guard is a problem associated with lawnmowers, and especially for lawnmowers comprising a cutting arrangement of the above-mentioned type. Poor evacuation of clippings accelerates build-up of clippings inside the cutting guard. Build-up of clipping on inside surfaces of a cutting guard can cause bending of cutting members of the cutting units, which compromises the cutting result and increases the energy-consumption of the cutting arrangement. One way to improve evacuation and spreading of clippings from the cutting guard could be to increase the power and the rotational speed of the cutting units of the cutting arrangement. However, as indicated above, it is for many reasons desirable to minimize the energy consumption of a cutting arrangement. Moreover, in many applications, there are practical and legal limitations on the power and rotational speeds of cutting units of cutting arrangements.

[0016] SUMMARY

[0017] It is an object of the present invention to overcome, or at least alleviate, at least some of the above-mentioned problems and drawbacks.

[0018] According to a first aspect of the invention, the object is achieved by a cutting arrangement configured to be attached to a lawnmower such that a forward direction of the cutting arrangement coincides with a forward direction of the lawnmower. The cutting arrangement comprises a cutting guard and a first cutting unit configured to rotate in a first rotational direction around a first rotation axis such that one or more radially outer portions of the first cutting unit orbits in a first circular path inside the cutting guard. The cutting arrangement further comprises a second cutting unit configured to rotate in a second rotational direction around a second rotation axis such that one or more radially outer portions of the second cutting unit orbits in a second circular path inside the cutting guard. The second rotational direction is opposite to the first rotational direction and the second circular path overlaps the first circular path such that an overlapping area is formed between the first and second circular paths. The cutting guard comprises a discharge opening arranged to eject clippings along a main discharge direction from the cutting guard. A tangential movement direction of the first and second cutting units coincides with the main discharge direction of the discharge opening at a location within the overlapping area upon rotation of the first and second cutting units around the respective first and second rotation axes.

[0019] Since the second rotational direction is opposite to the first rotational direction and the tangential movement direction of each of the first and second cutting units coincides with the main discharge direction within the overlapping area, a cutting arrangement is provided capable of evacuating and spreading clippings from the cutting guard in an efficient and even manner with a reduced risk of formation of strings or clumps on a lawn being mowed. This is because the tangential movement direction of the first and second cutting units generate airflow pulses within the overlapping area directed towards the discharge opening, which assists the evacuation and spreading of clippings from the cutting guard. Moreover, due to the features of the cutting arrangement, an efficient evacuation of clippings can be obtained from the cutting guard using a low amount of energy. Furthermore, the risk of build-up of clipping on inside surfaces of a cutting guard is reduced as a result of efficient evacuation of clippings from the cutting guard. Thereby, bending of cutting members of the first and second cutting units can be avoided which can ensure a clean cutting result and a low energy-consumption of the cutting arrangement.

[0020] Moreover, a cutting arrangement is provided having conditions for obtaining a clean and even cutting result upon movement in the forward direction thereof over a lawn. This is because the second circular path overlaps the first circular path which can ensure a clean and even cutting result also in the area between the first and second rotation axis of the cutting arrangement.

[0021] Accordingly, due to the features of the cutting arrangement, the energy consumption of a lawnmower comprising the cutting arrangement can be lowered while obtaining an efficient evacuation and spreading of clippings from the cutting arrangement as well as a clean and even cutting result. In addition, the cutting arrangement provides conditions for increasing available operational time of a lawnmower comprising the cutting arrangement before an energy storing unit of the lawnmower has to be charged or refilled. As a further result thereof, the cutting arrangement provides conditions for operating a lawnmower comprising the cutting arrangement in a more cost-efficient manner.

[0022] Accordingly, a cutting arrangement is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

[0023] Optionally, the angle between each of the first and the second rotation axes and the forward direction of the cutting arrangement is within the range of 78 - 102 degrees or is within the range of 83 - 97 degrees. Thereby, a clean and even cutting result can be further ensured as well as an efficient evacuation and spreading of clippings from the cutting arrangement. Moreover, conditions are provided for an energy-efficient cutting arrangement.

[0024] Optionally, the cutting arrangement is configured such that the angle between the forward direction of the cutting arrangement and a line passing through each of the first and second rotation axes is within the range of 75 - 105 degrees or is within the range of 85 - 95 degrees. Thereby, a clean and even cutting result can be ensured while obtaining a cutting arrangement having conditions for obtaining a significant cutting width upon movement of the cutting arrangement in the forward direction thereof over a lawn.

[0025] Optionally, the discharge opening is arranged at a rear portion of the cutting guard as seen relative to the forward direction of the cutting arrangement. Thereby, a cutting arrangement is provided having conditions for distributing clippings more evenly across the lawn while avoiding evacuation of clippings onto uncut areas of a lawn. Moreover, sidewalks and driveways can be kept free of clippings, as the clippings are ejected towards the rear portion of the cutting guard and not towards the side or front of the cutting guard.

[0026] Optionally, the discharge opening is funnel-shaped with an increasing width along the main discharge direction. Thereby, a cutting arrangement is provided capable of evacuating and spreading clippings from the cutting guard in an even more efficient and even manner with a further reduced risk of formation of strings or clumps on a lawn being mowed. Moreover, due to these features, it can be further ensured that clippings can be evacuated from the cutting guard in an energy-efficient manner.

[0027] Optionally, the discharge opening comprises two opposing delimiting walls, and wherein the angle between the forward direction of the cutting arrangement and each of the two opposing delimiting walls is within the range of 5 - 23 degrees or is within the range of 10 - 18 degrees. Thereby, it can be further ensured that clippings from the cutting guard can be evacuated and spread in an even more efficient and even manner a reduced risk of formation of strings or clumps on a lawn being mowed. Moreover, it can be further ensured that clippings can be evacuated from the cutting guard in an energy-efficient manner.

[0028] Optionally, the angle between the main discharge direction and the forward direction of the cutting arrangement is within the range of 155 - 205 degrees or is within the range of 175 - 185 degrees. Thereby, a cutting arrangement is provided having conditions for distributing clippings more evenly across the lawn while avoiding evacuation of clippings onto uncut areas of a lawn as the clippings are ejected in directions substantially opposite to the forward direction of the cutting arrangement. As a further result, sidewalks and driveways can be kept free of clippings, as the clippings are ejected in directions substantially opposite to the forward direction of the cutting arrangement and not towards the side or front of the cutting guard.

[0029] Optionally, the angle between the first and second rotation axis is less than 10 degrees or is less than 5 degrees. Thereby, a clean and even cutting result can be further ensured. Optionally, the cutting guard comprises a first cutting guard portion enclosing part of the first circular path and a second cutting guard portion enclosing part of the second circular path. Thereby, conditions are provided for a safe and energy-efficient cutting arrangement. This is because the first and second cutting guard portions can enhance the aerodynamic properties of the first and second cutting units respectively. These improvements help direct directing airflow generated by the rotating first and second cutting units, which can provide effective lifting of grass for cutting, as well as an effective evacuation and spreading clippings from the cutting arrangement, using a low amount of energy.

[0030] Optionally, the cutting guard is configured such that the distance between each of the first and second circular paths and a front section of the first and second cutting guard portions respectively is greater than the distance between each of the first and second circular paths and a rear section of the first and second cutting guard portions respectively. Thereby, a cutting arrangement is provided having conditions for cutting grass in an energy efficient manner while having conditions for obtaining an improved cutting result. The cutting result can be improved because grass is allowed to raise to an upright straight position by its own stiffness after having been bent by a respective front section of the first and second cutting guard portions during movement of the cutting guard in the forward direction of the cutting arrangement over a lawn.

[0031] That is, studies have shown that the bending of the grass caused by the front section of a cutting guard impairs the cutting result because a large proportion of the grass do not have time to raise to an upright straight position by its own stiffness to reach the cutting unit. However, due to the greater distance between each of the first and second circular paths and a front section of the first and second cutting guard portions, at least a larger proportion of the grass will have time to raise to an upright straight position by its own stiffness after having been bent by the respective front section of the first and second cutting guard portions. Thereby, conditions are provided for an improved cutting result.

[0032] Moreover, the need for forming a large negative pressure inside the first and second cutting guard portions is circumvented, or at least reduced, which provides conditions for operating the cutting arrangement in an energy efficient manner. In addition, the greater distance between each of the first and second circular paths and a front section of the first and second cutting guard portions can reduce the negative pressure inside the cutting guard which in turn can reduce the rotational resistance of the cutting unit and hence the energy consumption of the cutting unit. Thus, due to the features of the cutting arrangement, the energy consumption of a lawnmower comprising the cutting arrangement can be lowered and the cutting result can be improved. In addition, the cutting arrangement provides conditions for increasing available operational time of a lawnmower comprising the cutting arrangement before an energy storing unit of the lawnmower has to be charged or refilled. As a further result thereof, the cutting arrangement provides conditions for operating a lawnmower comprising the cutting arrangement in a more cost-efficient manner.

[0033] Optionally, the first cutting guard portion is configured such that the distance between the first rotation axis and radially inner delimiting surfaces of the first cutting guard portion increases continuously, seen in the first rotational direction, within a first angle having its vertex at the first rotation axis, and wherein the first angle exceeds 90 degrees, or exceeds 180 degrees, wherein the second cutting guard portion is configured such that the distance between the second rotation axis and radially inner delimiting surfaces of the second cutting guard portion increases continuously, seen in the second rotational direction, within a second angle having its vertex at the second rotation axis, and wherein the second angle exceeds 90 degrees, or exceeds 180 degrees. Thereby, efficient aerodynamic properties can be provided inside the first and second cutting guard portions. In this manner, it can be ensured that an airflow and a negative pressure inside the first and second cutting guard portions can be generated in an efficient manner to lower the energy consumption of the cutting arrangement, improve the cutting result thereof, and obtain an efficient evacuation and spreading of clippings from the cutting arrangement.

[0034] Optionally, the radially inner delimiting surfaces of the first cutting guard portion extend in directions substantially parallel to the first rotation axis, and wherein the radially inner delimiting surfaces of the second cutting guard portion extend in directions substantially parallel to the second rotation axis. Thereby, conditions are provided for generating a negative pressure inside the first and second cutting guard portions in an efficient manner to lower the energy consumption of the cutting arrangement, improve the cutting result thereof, and obtain an efficient evacuation and spreading of clippings from the cutting arrangement.

[0035] Optionally, the cutting guard comprises a top surface, a first centre body protruding from the top surface inside the first cutting guard portion, and a second centre body protruding from the top surface inside the second cutting guard portion. Thereby, further improved aerodynamic properties can be provided inside the first and second cutting guard portions. In this manner, it can be further ensured that an airflow and a negative pressure inside the first and second cutting guard portions can be generated in an efficient manner to lower the energy consumption of the cutting arrangement, improve the cutting result thereof, and obtain an efficient evacuation and spreading of clippings from the cutting arrangement. The feature that the first and second centre bodies protrude from the top surface means that each of the first and second centre bodies protrudes from the top surface in a direction towards a ground surface when the cutting arrangement is attached to a lawnmower and the lawnmower is positioned onto the ground surface in an intended use position.

[0036] Optionally, radially outer delimiting surfaces of the first centre body extends in directions substantially parallel to the first rotation axis, and wherein radially outer delimiting surfaces of the second centre body extends in directions substantially parallel to the second rotation axis. Thereby, conditions are provided for generating a negative pressure inside the first and second cutting guard portions respectively in an efficient manner to lower the energy consumption of the cutting arrangement, improve the cutting result thereof, and obtain an efficient evacuation and spreading of clippings from the cutting arrangement.

[0037] Optionally, the height of the radially outer delimiting surfaces of the first centre body is at least 20%, or is at least 50%, of the height of the radially inner delimiting surfaces of the first cutting guard portion, and wherein the height of the radially outer delimiting surfaces of the second centre body is at least 20%, or is at least 50%, of the height of the radially inner delimiting surfaces of the second cutting guard portion. Thereby, it can be further ensured that a negative pressure can be generated in an energy-efficient manner inside the first and second cutting guard portions respectively to lower the energy consumption of the cutting arrangement, improve the cutting result thereof, and obtain an efficient evacuation and spreading of clippings from the cutting arrangement.

[0038] Optionally, the first centre body is configured such that the distance from the first rotation axis to radially outer delimiting surfaces of the first centre body decreases continuously, seen in the first rotational direction, within a third angle having its vertex at the first rotation axis, and wherein the third angle exceeds 90 degrees, or exceeds 180 degrees, and wherein the second centre body is configured such that the distance from the second rotation axis to radially outer delimiting surfaces of the second centre body decreases continuously, seen in the second rotational direction, within a fourth angle having its vertex at the second rotation axis, and wherein the fourth angle exceeds 90 degrees, or exceeds 180 degrees. Thereby, even further improved aerodynamic properties can be provided inside the first and second cutting guard portions. In this manner, it can be further ensured that an airflow and a negative pressure inside the first and second cutting guard portions can be generated in an efficient manner to lower the energy consumption of the cutting arrangement, improve the cutting result thereof, and obtain an efficient evacuation and spreading of clippings from the cutting arrangement.

[0039] Optionally, the discharge opening comprises two opposing delimiting walls each adjoining one of the first and second centre bodies. Thereby, a continuous airflow can be ensured towards the discharge opening upon rotation of the first and second cutting units around their respective rotation axis. As a result, an efficient evacuation and spreading of clippings from the cutting arrangement can be further ensured using a low amount of energy.

[0040] Optionally, the cutting arrangement comprises a motor assembly configured to rotate the first and second cutting units at synchronized rotational speeds. Thereby, impacts between cutting members of the first and second cutting units can be avoided in an efficient manner thereby ensuing durability of the cutting arrangement.

[0041] Optionally, the motor assembly comprises a first electric motor configured to rotate the first cutting unit, a second electric motor configured to rotate the second cutting unit, and a control arrangement configured to operate the first and second electric motors at synchronized rotational speeds. Thereby, impacts between cutting members of the first and second cutting units can be avoided in an efficient manner while circumventing the need for a mechanical arrangement linking the rotation of the first and second cutting units. In this manner, a less complex and more durable cutting arrangement can be provided having a low weight. Moreover, a more environmentally friendly cutting arrangement can be provided having conditions for generating less noise.

[0042] Optionally, each of the first and second cutting units comprises one or more surfaces being angled relative to a rotation plane of the cutting unit to generate an airflow in a direction transverse to the rotation plane during rotation of the cutting unit. Thereby, a cutting arrangement is provided having conditions for generating airflow and a negative pressure inside the first and second cutting guard portions respectively in an energy efficient manner to lift grass towards the first and second cutting units. Moreover, due to the form of cutting guard according to some embodiments providing conditions for generating airflow and negative pressure in an efficient manner, the need for using large angles of the surfaces is reduced. In this manner, a low rotational resistance of the first and second cutting units can be provided to lower the energy consumption of the cutting arrangement. Optionally, the surfaces are angled relative to the rotation plane to generate an airflow in a direction towards the top surface of the cutting guard during rotation of the first and second cuttings units in the first and second rotational directions respectively. Thereby, an airflow is generated in directions from the ground surface towards the top surface of the cutting guard during operation of the cutting arrangement to efficiently lift grass towards the first and second cutting units respectively.

[0043] Optionally, each of the first and second cutting units comprises a hub and a number of cutting members pivotally attached at a periphery of the hub. Thereby, a safer and more durable cutting arrangement is provided because a cutting member may pivot upon impact with an object, such as a stone, a stump, or a limb of a person or animal.

[0044] Optionally, the one or more surfaces are surfaces of the cutting members. Thereby, a safer and more durable cutting arrangement is provided having conditions for efficiently generating a negative pressure inside the cutting guard.

[0045] Optionally, the hub is disc shaped. Thereby, an even safer and more operational reliable cutting arrangement is provided. This is because a disc shaped hub is considerably less likely to become stuck upon impact with an object, such as a stone, a stump, or a limb of a person or animal, as compared to a hub having another type of shape.

[0046] According to a second aspect of the invention, the object is achieved by a lawnmower comprising a cutting arrangement according to some embodiments of the present disclosure.

[0047] Thereby, a lawnmower is provided capable of evacuating and spreading clippings from the cutting guard of the cutting arrangement in an efficient and even manner with a reduced risk of formation of strings or clumps on a lawn being mowed.

[0048] Moreover, due to the features of the cutting arrangement of the lawnmower, an efficient evacuation of clippings can be obtained from the cutting guard of the lawnmower using a low amount of energy. Furthermore, the risk of build-up of clipping on inside surfaces of a cutting guard is reduced as a result of efficient evacuation of clippings from the cutting guard.

[0049] Thereby, bending of cutting members of the first and second cutting units can be avoided which can ensure a clean cutting result and a low energy-consumption of the lawnmower.

[0050] Moreover, a lawnmower is provided having conditions for obtaining a clean and even cutting result upon movement in the forward direction thereof over a lawn. This is because the second circular path overlaps the first circular path which can ensure a clean and even cutting result also in an area between the first and second rotation axis of the cutting arrangement.

[0051] Accordingly, the energy consumption of the lawnmower can be lowered while obtaining an efficient evacuation and spreading of clippings from the cutting arrangement as well as a clean and even cutting result. In addition, an available operational time of the lawnmower can be increased before an energy storing unit of the lawnmower has to be charged or refilled. Moreover, the lawnmower can be operated in a more cost-efficient manner.

[0052] Accordingly, a lawnmower is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

[0053] Optionally, the lawnmower is a self-propelled robotic lawnmower configured to navigate and cut grass in an area in an autonomous manner. Thereby, a self-propelled robotic lawnmower is provided capable of evacuating and spreading clippings from the cutting guard of the cutting arrangement in an efficient and even manner with a reduced risk of formation of strings or clumps on a lawn being mowed.

[0054] Moreover, due to the features of the cutting arrangement of the self-propelled robotic lawnmower, an efficient evacuation of clippings can be obtained from the cutting guard thereof using a low amount of energy. Furthermore, the risk of build-up of clipping on inside surfaces of a cutting guard is reduced as a result of efficient evacuation of clippings from the cutting guard. Thereby, bending of cutting members of the first and second cutting units can be avoided which can ensure a clean cutting result and a low energy-consumption of the self-propelled robotic lawnmower.

[0055] Moreover, a self-propelled robotic lawnmower is provided having conditions for obtaining a clean and even cutting result upon movement in the forward direction thereof over a lawn. This is because the second circular path overlaps the first circular path which can ensure a clean and even cutting result also in an area between the first and second rotation axis of the cutting arrangement.

[0056] Accordingly, the energy consumption of the self-propelled robotic lawnmower can be lowered while obtaining an efficient evacuation and spreading of clippings from the cutting arrangement as well as a clean and even cutting result. In addition, an available operational time of the self-propelled robotic lawnmower can be increased before an energy storing unit of the self-propelled robotic lawnmower has to be charged or refilled. Moreover, the self- propelled robotic lawnmower can be operated in a more cost-efficient manner.

[0057] Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description.

[0058] BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Various aspects of the invention, including its particular features and advantages, will be readily understood from the example embodiments discussed in the following detailed description and the accompanying drawings, in which:

[0060] Fig. 1 illustrates a side view of a lawnmower according to some embodiments, Fig. 2 illustrates a view of an underside of the lawnmower illustrated in Fig. 1 , Fig. 3 illustrates a first enlarged view of an underside of a cutting arrangement of the lawnmower illustrated in Fig. 1 and Fig. 2,

[0061] Fig. 4 illustrates a second enlarged view of the underside of the cutting arrangement of the lawnmower illustrated in Fig. 1 and Fig. 2,

[0062] Fig. 5 illustrates a cross section of the cutting arrangement illustrated in Fig. 4, and Fig. 6 illustrates a cross section of the cutting arrangement illustrated in Fig. 3.

[0063] DETAILED DESCRIPTION

[0064] Aspects of the present invention will now be described more fully. Like reference signs refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and / or clarity.

[0065] Fig. 1 illustrates a side view of a lawnmower 1 according to some embodiments of the present disclosure. According to the illustrated embodiments, the lawnmower 1 is a self- propelled autonomous robotic lawnmower, i.e. a lawnmower 1 capable of navigating and operating in an autonomous manner in an area without the intervention or the direct control of a user. For reasons of brevity and clarity, the self-propelled autonomous robotic lawnmower 1 is in some places herein referred to as “the robotic lawnmower 1” or simply “the lawnmower 1”. According to further embodiments, the lawnmower 1, as referred to herein, may be another type of lawnmower, such as a walk-behind mower or a push mower.

[0066] According to the embodiments herein, the lawnmower 1 is a small or mid-sized lawnmower 1 configured to be 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.

[0067] The lawnmower 1 comprises a lawnmower body 30 and a number of lawnmower support members 6, 4 each configured to abut against a ground surface G in a first plane P1 during operation of the lawnmower 1 to support the lawnmower body 30. The lawnmower body 30, as referred to herein, may also be referred to as a lawnmower chassis. Accordingly, the first plane P1 will extend along a ground surface G when the lawnmower 1 is positioned on a flat ground surface G in an intended use position thereon as is illustrated in Fig. 1.

[0068] In Fig. 1 , a longitudinal direction Id of the lawnmower 1 is indicated. The longitudinal direction Id of the lawnmower 1 extends in a longitudinal plane of the lawnmower 1. The longitudinal plane is parallel to the first plane P1. The longitudinal direction Id of the lawnmower 1 is thus parallel to the first plane P1 and thus also to a ground surface G when the lawnmower 1 is positioned onto a flat ground surface G in an intended use position. Moreover, the longitudinal direction Id of the lawnmower 1 is parallel to a forward direction fd’ of the lawnmower 1 as well as a reverse direction of the lawnmower 1. The reverse direction is opposite to the forward direction fd’. The forward direction fd’ of the lawnmower 1 may also be referred to as a forward moving direction fd’ of the lawnmower 1. Likewise, the reverse direction of the lawnmower 1 may also be referred to as a reverse moving direction of the lawnmower 1.

[0069] Fig. 2 illustrates a view of an underside of the lawnmower 1 illustrated in Fig. 1. Below, simultaneous reference is made to Fig. 1 and Fig. 2, if not indicated otherwise.

[0070] According to the illustrated embodiments, the lawnmower support members 6, 4 is wheels 6, 4 of the lawnmower 1. Moreover, as is best seen in Fig. 2, according to the illustrated embodiments, the lawnmower 1 comprises four wheels 6, 4, namely two drive wheels 6 and two support wheels 4. The drive wheels 6 of the lawnmower 1 may each be powered by an electrical motor of the lawnmower 1 to provide motive power and / or steering of the lawnmower 1.

[0071] According to the illustrated embodiments, the drive wheels 6 of the lawnmower 1 are nonsteered wheels having a fix rolling direction in relation to the lawnmower body 30. The respective rolling direction of the drive wheels 6 of the lawnmower 1 is substantially parallel to the longitudinal direction Id of the lawnmower 1. According to the illustrated embodiments, the support wheels 4 are non-driven wheels. Moreover, according to the illustrated embodiments, the support wheels 4 are pivotally arranged around a respective pivot axis such that the rolling direction of the respective support wheel 4 can follow a travel direction of the lawnmower 1.

[0072] As understood from the above, when the drive wheels 6 of the lawnmower 1 are rotated at the same rotational velocity in a forward rotational direction, and no wheel slip is occurring, the lawnmower 1 will move in the forward direction fd’ indicated in Fig. 1. Likewise, when the drive wheels 6 of the lawnmower 1 are rotated at the same rotational velocity in a reverse rotational direction, and no wheel slip is occurring, the lawnmower 1 will move in the reverse direction.

[0073] 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 lawnmower 1 may be provided with another number of wheels 6, 4, such as three wheels. Moreover, according to further embodiments, the lawnmower 1 may be provided with another configuration of driven and non-driven wheels, such as a front wheel drive or an all-wheel drive.

[0074] According to the illustrated embodiments, the lawnmower 1 comprises a control arrangement 28. The control arrangement 28 may be configured to control propulsion of the lawnmower 1, and steer the lawnmower 1, by controlling electrical motors of the lawnmower 1 arranged to drive the drive wheels 6 of the lawnmower 1. According to further embodiments, the control arrangement 28 may be configured to steer the lawnmower 1 by controlling the angle of steered wheels of the lawnmower 1. According to still further embodiments, the robotic lawnmower may be an articulated robotic lawnmower, wherein the control arrangement 28 may be configured to steer the robotic lawnmower by controlling the angle between frame portions of the articulated robotic lawnmower.

[0075] The control arrangement 28 may be configured to control propulsion of the lawnmower 1 and may be configured to 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 magnetic field of a wire, and / or one or more positioning units, and / or one or more sensors arranged to detect an impending or ongoing collision event with an object. In addition, the lawnmower 1 may comprise a communication unit connected to the control arrangement 28. The communication unit may be configured to communicate with a remote communication unit to receive instructions therefrom and / or to send information thereto. The communication may be performed wirelessly over a wireless connection such as the internet, or a wireless local area network (WLAN), or a cellular network, or a wireless connection for exchanging data 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 2.486 GHz.

[0076] As an alternative, or in addition, the control arrangement 28 may be configured to obtain data from, or may comprise, one or more positioning units utilizing a local reference source, such as a local sender and / or a wire, to estimate or verify a current position of the lawnmower 1. As another example, the lawnmower 1 may comprise one or more of a Radio Detection and Ranging (radar) sensor, a Light Detection and Ranging (lidar) sensor, an image capturing unit, such as a camera, an ultrasound sensor, or the like.

[0077] The control arrangement 28 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 / or random pattern to ensure that an area is completely covered, using input from one or more of the above described sensors and / or units. Furthermore, the lawnmower 1 may comprise one or more batteries arranged to supply electricity to components of the lawnmower 1. As an example, the one or more batteries may be arranged to supply electricity to electrical motors of the lawnmower 1, such as one or more electric propulsion motors, by an amount controlled by the control arrangement 28.

[0078] As indicated in Fig. 1 and Fig. 2, the lawnmower 1 comprises a cutting arrangement 2. The cutting arrangement 2 is configured to cut vegetation, such as grass, as is further explained herein. In Fig. 1 and Fig. 2, the cutting arrangement 2 is attached to the lawnmower 1 such that a forward direction fd of the cutting arrangement 2 coincides with the forward direction fd’ of the lawnmower 1. The forward direction fd of the cutting arrangement 2 is indicated in Fig. 2.

[0079] In more detail, according to the illustrated embodiments, the cutting arrangement 2 is attached to the lawnmower 1 by a number of fastening elements protruding through mounting portions 16 of the cutting arrangement 2 into holes of the lawnmower body 30 of the lawnmower 1. As an alternative, or in addition, the cutting arrangement 2 may be attached to the lawnmower 1 using one or more snap-fit arrangements, or the like. As understood from the above described, according to the illustrated embodiments, the cutting arrangement 2 is configured to be attached to the lawnmower body 30 in a predetermined orientation relative to the lawnmower body 30 via the mounting portions 16 of the cutting arrangement 2. As is indicated in Fig. 1 and Fig. 2, according to the illustrated embodiments, the lawnmower body 30 comprises a front section 13 acting as an external cover for the cutting arrangement 2. In these embodiments, the cutting arrangement 2 is attached to the lawnmower 1 by a number of fastening elements protruding through the mounting portions 16 of the cutting arrangement 2 into holes of the front section 13 of the lawnmower body 30. According to further embodiments, the lawnmower 1 may be configured in another manner.

[0080] As is best seen in Fig. 2, the cutting arrangement 2 comprises a cutting guard 3 and a first and a second cutting unit 11 , 12. The first cutting unit 11 is configured to rotate in a first rotational direction r1 around a first rotation axis ax1 and the second cutting unit 12 is configured to rotate in a second rotational direction r2 around a second rotation axis ax2. As indicated in Fig. 2, the second rotational direction r2 is opposite to the first rotational direction r1. According to the illustrated embodiments, the second rotation axis ax2 is parallel to the first rotation axis ax1. In other words, according to the illustrated embodiments, the first and second rotation axis ax1, ax2 are parallel to each other. According to further embodiments, the angle between the first and second rotation axis ax2 may be less than 10 degrees or may be less than 5 degrees.

[0081] Moreover, as is schematically indicated in Fig. 1 , the cutting arrangement 2 comprises a motor assembly 7. The motor assembly 7 is configured to rotate the first and second cutting units 11 , 12 at synchronized rotational speeds, as is further explained herein. Further features and functions of the motor assembly 7 is explained with reference to Fig. 5 and Fig. 6 below.

[0082] Fig. 3 illustrates a first enlarged view of an underside of the cutting arrangement 2 of the lawnmower 1 illustrated in Fig. 1 and Fig. 2. Below, simultaneous reference is made to Fig. 1 - Fig. 3, if not indicated otherwise. The cutting arrangement 2, as referred to herein, may be provided and may be sold as a separate unit, wherein the cutting arrangement 2 is configured to be attached to a lawnmower 1 such that a forward direction fd of the cutting arrangement 2 coincides with a forward direction fd’ of the lawnmower 1. Also in Fig. 3, the mounting portions 16 of the cutting arrangement 2 have been indicated. The mounting portions 16 facilitate an attachment of the cutting arrangement 2 to a lawnmower 1. Moreover, in Fig. 3, the forward direction fd of the cutting arrangement 2 has been indicated.

[0083] As indicated in Fig. 3, the first cutting unit 11 is configured to rotate in the first rotational direction r1 around the first rotation axis ax1 such that one or more radially outer portions 1 T of the first cutting unit 11 orbits in a first circular path c1 inside the cutting guard 3. Moreover, the second cutting unit 12 configured to rotate in the second rotational direction r2 around the second rotation axis ax2 such that one or more radially outer portions 12’ of the second cutting unit 12 orbits in a second circular path c2 inside the cutting guard 3. As mentioned with reference to Fig. 2, the second rotational direction r2 is opposite to the first rotational direction r1.

[0084] Moreover, as indicated in Fig. 3, the second circular path c2 overlaps the first circular path c1 such that an overlapping area A is formed between the first and second circular paths c1, c2. The overlapping area A, as referred to herein, is an area between the first and second circular paths as seen in a direction coinciding with the first and second rotation axes ax1, ax2. The cutting guard 3 further comprises a discharge opening 5 arranged to eject clippings along a main discharge direction md from the cutting guard 3. As is indicated in Fig. 3, the cutting arrangement 2 is configured such that a tangential movement direction T1 of the first cutting unit 11 coincides with the main discharge direction md at a location within the overlapping area A upon rotation of the first cutting unit 11 around the first rotation axis ax1 in the first rotational direction r1.

[0085] Fig. 4 illustrates a second enlarged view of the underside of the cutting arrangement 2 of the lawnmower 1 illustrated in Fig. 1 and Fig. 2. Below, simultaneous reference is made to Fig. 1 - Fig. 4, if not indicated otherwise. In Fig. 4, each of the first and second cutting units 11, 12 has been rotated 90 degrees in the respective first and second rotational directions r1 , r2 by the motor assembly 7 indicated in Fig. 1 as compared to the rotational positions of the first and second cutting units 11, 12 illustrated in Fig. 3.

[0086] As is indicated in Fig. 4, the cutting arrangement 2 is configured such that a tangential movement direction T2 of the second cutting unit 12 coincides with the main discharge direction md at a location within the overlapping area A upon rotation of the second cutting unit 12 around the second rotation axis ax2 in the second rotational direction r2.

[0087] In other words, the cutting arrangement 2 is configured such that a tangential movement direction T1 , T2 of each of the first and second cutting units 11, 12 coincides with the main discharge direction md at a location within the overlapping area A upon rotation of the first and second cutting units 11, 12 around the respective first and second rotation axes ax1, ax2 in the respective first and second rotational directions r1, r2. As a result, airflow pulses are generated within the overlapping area A, wherein the airflow pulses are directed towards the discharge opening 5. The airflow pulses from the overlapping area A assist the evacuation and spreading of clippings from the cutting guard 3.

[0088] Moreover, due to the features of the cutting arrangement 2, an efficient evacuation of clippings can be obtained from the cutting guard 3 using a low amount of energy. Furthermore, the risk of build-up of clipping on inside surfaces of a cutting guard 3 is reduced as a result of efficient evacuation of clippings from the cutting guard 3. Thereby, bending of cutting members 61 , 62 of the first and second cutting units 11, 12 can be avoided which can ensure a clean cutting result and a low energy-consumption of the cutting arrangement 2.

[0089] Moreover, a cutting arrangement 2 is provided having conditions for obtaining a clean and even cutting result upon movement in the forward direction fd thereof over a lawn. This is because the second circular path c2 overlaps the first circular path c1 which can ensure a clean and even cutting result also in an area between the first and second rotation axis ax1, ax2 of the cutting arrangement 2.

[0090] Accordingly, due to the features of the cutting arrangement 2, the energy consumption of a lawnmower 1 comprising the cutting arrangement 2 can be lowered while obtaining an efficient evacuation and spreading of clippings from the cutting arrangement 2 and a clean and even cutting result. In addition, the cutting arrangement 2 provides conditions for increasing available operational time of a lawnmower 1 comprising the cutting arrangement 2 before an energy storing unit of the lawnmower 1 has to be charged or refilled. As a further result thereof, the cutting arrangement 2 provides conditions for operating a lawnmower 1 comprising the cutting arrangement 2 in a more cost-efficient manner.

[0091] As indicated in Fig. 3 and Fig. 4, according to the illustrated embodiments, the cutting arrangement 2 is configured such that the angle a2 between the forward direction fd of the cutting arrangement 2 and a line L passing through each of the first and second rotation axes ax1 , ax2 is 90 degrees. In other words, according to the illustrated embodiments, the first and second cutting units 11, 12, as well as the first and second rotation axes ax1 , ax2 thereof, are arranged side by side as seen relative to the forward direction fd of the cutting arrangement 2. According to further embodiments, the cutting arrangement 2 may be configured such that the angle a2 between the forward direction fd of the cutting arrangement 2 and a line L passing through each of the first and second rotation axes ax1, ax2 is within the range of 75 - 105 degrees or is within the range of 85 - 95 degrees. Moreover, according to the illustrated embodiments, the discharge opening 5 is arranged at a rear portion 3’ of the cutting guard 3 as seen relative to the forward direction fd of the cutting arrangement 2. The rear portion 3’ of the cutting guard 3 forms a trailing portion of the cutting guard 3 upon movement of the cutting arrangement 2 in the forward direction fd of the cutting arrangement 2.

[0092] According to the illustrated embodiments, the angle a4 between the main discharge direction md and the forward direction fd of the cutting arrangement 2 is 180 degrees. According to further embodiments, the angle a4 between the main discharge direction md and the forward direction fd of the cutting arrangement 2 may be within the range of 155 - 205 degrees or may be within the range of 175 - 185 degrees.

[0093] Moreover, as can be seen in Fig. 3 and Fig. 4, according to the illustrated embodiments, the discharge opening 5 is funnel-shaped with an increasing width w along the main discharge direction md. The discharge opening 5 comprises two opposing delimiting walls 15, 17. The feature that the discharge opening 5 comprises two opposing delimiting walls 15, 17 means that the cutting guard 3 comprises two opposing delimiting walls 15, 17 arranged to face each other on a respective side of the discharge opening 5, wherein each of the two opposing delimiting walls 15, 17 forms a delimiting surface of the discharge opening 5.

[0094] According to the illustrated embodiments, the angle a3 between the forward direction fd of the cutting arrangement 2 and each of the two opposing delimiting walls 15, 17 is approximately 14 degrees. According to further embodiments, the angle a3 between the forward direction fd of the cutting arrangement 2 and each of the two opposing delimiting walls 15, 17 may be within the range of 5 - 23 degrees or may be within the range of 10 - 18 degrees.

[0095] The cutting guard 3 according to the illustrated embodiments comprises a first cutting guard portion 31 and a second cutting guard portion 32. The first cutting guard portion 31 encloses part of the first circular path c1 and the second cutting guard portion 32 enclosing part of the second circular path c2.

[0096] Moreover, according to the illustrated embodiments, the cutting guard 3 is configured such that the distance d1, dT between each of the first and second circular paths c1, c2 and a front section 3T, 32’ of the first and second cutting guard portions 31, 32 respectively is greater than the distance d2, d2’ between each of the first and second circular paths c1, c2 and a rear section 31”, 32” of the first and second cutting guard portions 31 , 32 respectively. Thereby, grass is allowed to raise to an upright straight position by its own stiffness after having been bent by the respective front section 3T, 32’ of the first and second cutting guard portions 31, 32 during movement of the cutting guard 3 in the forward direction fd of the cutting arrangement 1 over a lawn. In this manner, a clean and even cut of grass can be obtained while only generating a low negative pressure inside the first and second cutting guard portions 31, 32, as is further explained herein.

[0097] According to the illustrated embodiments, the cutting guard 3 is configured such that the distance d1, dT between each of the first and second circular paths c1, c2 and a front section 3T, 32’ of the first and second cutting guard portions 31, 32 respectively is approximately seven times greater than the distance d2, d2’ between each of the first and second circular paths c1, c2 and a rear section 31”, 32” of the first and second cutting guard portions 31, 32 respectively. According to further embodiments, the cutting guard 3 may be configured such that the distance d1, dT between each of the first and second circular paths c1, c2 and a front section 3T, 32’ of the first and second cutting guard portions 31 , 32 respectively is at least more than three times greater than the distance d2, d2’ between each of the first and second circular paths c1, c2 and a rear section 31”, 32” of the first and second cutting guard portions 31 , 32 respectively.

[0098] A front section 3T, 32’ of the first and second cutting guard portions 31, 32 forms a leading section of the first and second cutting guard portions 31 , 32 upon movement of the cutting arrangement 2 in the forward direction fd of the cutting arrangement 2. A rear section 31”, 32” of the first and second cutting guard portions 31 , 32 forms a trailing section of the first and second cutting guard portions 31, 32 upon movement of the cutting arrangement 2 in the forward direction fd of the cutting arrangement 2.

[0099] As is indicated in Fig. 3 and Fig. 4, according to the illustrated embodiments, the first cutting guard portion 31 is configured such that the distance d41 between the first rotation axis ax1 and radially inner delimiting surfaces 41 of the first cutting guard portion 31 increases continuously, seen in the first rotational direction r1, within a first angle e1 having its vertex v1 at the first rotation axis ax1. Likewise, according to the illustrated embodiments, the second cutting guard portion 32 is configured such that the distance d42 between the second rotation axis ax2 and radially inner delimiting surfaces 42 of the second cutting guard portion 32 increases continuously, seen in the second rotational direction r2, within a second angle e2 having its vertex v2 at the second rotation axis ax2. According to the embodiments illustrated in Fig. 3 and Fig. 4, each of the first and second angles e1 , e2 is approximately 226 degrees. According to further embodiments, one or both of the first and second angles e1 , e2 may exceed 90 degrees, or may exceed 180 degrees.

[0100] These features of the cutting guard 3 provide efficient aerodynamic properties inside the first and second cutting guard portions 31 , 32. In this manner, it can be ensured that an airflow and a negative pressure inside the first and second cutting guard portions 31, 32 can be generated in an efficient manner to lower the energy consumption of the cutting arrangement, improve the cutting result thereof, and obtain an efficient evacuation and spreading of clippings from the cutting arrangement 2.

[0101] According to the illustrated embodiments, the cutting guard 3 is symmetrical on either side of a plane positioned between the first and second cutting guard portions 31, 32, wherein the plane is parallel to each of the first and second rotation axis ax1, ax2 and to the forward direction fd of the cutting arrangement 2. In other words, according to the illustrated embodiments, the second cutting guard portion 32 has a substantially identical but mirrored layout and design as the first cutting guard portion 31. According to further embodiments, the cutting guard 3, and the first and second cutting guard portions 31, 32 thereof, may be configured differently.

[0102] Fig. 5 illustrates a cross section of the cutting arrangement 2 illustrated in Fig. 4. In Fig. 5, the cross section is made a location of the first rotation axis ax1 in a plane being parallel to each of the first rotation axis ax1 and the forward direction fd of the cutting arrangement 2.

[0103] Moreover, in Fig. 5, a first electric motor ml of the motor assembly 7 can be seen. The first electric motor ml is configured to rotate the first cutting unit 11 around the first rotation axis ax1. According to the illustrated embodiments an output shaft of the first electric motor ml is directly connected to the first cutting unit 11. In other words, according to the illustrated embodiments, the first electric motor ml is configured to rotate the first cutting unit 11 directly, without the use a transmission with a transmission ratio between the output shaft and the first cutting unit 11.

[0104] According to further embodiments, an output shaft of the first electric motor ml may be connected to the first cutting unit 11 via one or more transmission devices, wherein the one or more transmission devices may provide a transmission ratio between the output shaft of the first electric motor ml and the first cutting unit 11. Fig. 6 illustrates a cross section of the cutting arrangement 2 illustrated in Fig. 3. In Fig. 6, the cross section is made a location of the second rotation axis ax2 in a plane being parallel to each of the second rotation axis ax2 and the forward direction fd of the cutting arrangement 2.

[0105] Moreover, in Fig. 6, a second electric motor m2 of the motor assembly 7 can be seen. The second electric motor m2 is configured to rotate the second cutting unit 12 around the second rotation axis ax2. According to the illustrated embodiments an output shaft of the second electric motor m2 is directly connected to the second cutting unit 12. In other words, according to the illustrated embodiments, the second electric motor m2 is configured to rotate the second cutting unit 12 directly, without the use a transmission with a transmission ratio between the output shaft of the second electric motor m2 and the second cutting unit 12.

[0106] According to further embodiments, an output shaft of the second electric motor m2 may be connected to the second cutting unit 12 via one or more transmission devices, wherein the one or more transmission devices may provide a transmission ratio between the output shaft of the second electric motor m2 and the second cutting unit 12. Each of the first and second electric motors ml, m2 may be powered using electricity from a battery of the lawnmower 1.

[0107] Below, simultaneous reference is made to Fig. 1 - Fig. 6, if not indicated otherwise. As is schematically indicated in Fig. 1, the cutting arrangement 2 comprises a control arrangement 23. The control arrangement 23 is configured to operate the first and second electric motors ml, m2 at synchronized rotational speeds. The control arrangement 23 may also be referred to as a motor control arrangement.

[0108] The control arrangement 23 may be configured to synchronize the rotational speeds of the first and second electric motors ml, m2 using electronic synchronization, i.e. , may be configured to ensure that the electric power supplied to both of the first and second electric motors ml, m2 is equal and / or phase-matched, causing them to rotate at the same speed. The control of the first and second electric motors ml , m2 may be performed such that when one motor gets a higher load so that the speed drops, the other follows to the same speed. This type of control can be made very fast, such as within a few milli seconds, to hold the synchronization. Each of the first and second electric motors ml, m2 may be a synchronous motor. As the name suggests, synchronous motors are designed to operate at a constant speed that is synchronized with the frequency of the electrical supply. These motors are inherently capable of precise speed control and are therefore good candidates for electronic synchronization.

[0109] According to further embodiments, the motor assembly 7 may be configured to rotate the first and second cutting units 11, 12 at synchronized rotational speeds in another manner than described above. As an example, the motor assembly 7 may comprise one motor only for rotating the first and second cutting units 11, 12 around the respective first and second rotation axis ax1, ax2. According to such embodiments, first and second cutting units 11, 12 may be rotationally linked to each other via a transmission assembly. Moreover, according to some further embodiments, the motor assembly 7 may comprise one or more motors of another type than electric motors, such as one or more internal combustion engines.

[0110] According to the illustrated embodiments, each of the first and second cutting units 11, 12 comprises a hub 51 , 52 and a number of cutting members 61 , 62 pivotally attached at a periphery of the hub 51, 52. In more detail, as is best seen in Fig. 3 and Fig. 4, according to the illustrated embodiments, each of the first and second cutting units 11, 12 comprises a hub 51, 52 and two cutting members 61, 62 pivotally attached at a periphery of the hub 51, 52, wherein the two cutting members 61, 62 are arranged at opposite sides of the respective hub 51 , 52. According to further embodiments, each of the first and second cutting units 11 , 12 may comprise another number of cutting members 61, 62, such as tree or four.

[0111] Moreover, as is best seen in Fig. 3 and Fig. 4, the radially outer portions 1 T, 12’ of the first and second cutting units 11, 12 respectively are portions of the cutting members 61 , 62 of the first and second cutting units 11, 12.

[0112] As is indicated in Fig. 5, according to the illustrated embodiments, the radially inner delimiting surfaces 41 of the first cutting guard portion 31 extend in directions Di substantially parallel to the first rotation axis ax1. Likewise, as is indicated in Fig. 6, according to the illustrated embodiments, the radially inner delimiting surfaces 42 of the second cutting guard portion 32 extend in directions Di’ substantially parallel to the second rotation axis ax2. The wording “substantially parallel to”, as used herein, may encompass that the angle between the objects referred to is less than 10 degrees, or is less than 7 degrees.

[0113] As indicated in Fig. 5 and Fig. 6, the cutting guard 3 comprises a top surface 33. According to the illustrated embodiments, the top surface 33 of the cutting guard 3 is substantially parallel to the first plane P1 and thus also to a ground surface G when the lawnmower 1 is positioned onto a flat ground surface G in the intended use position. Moreover, as indicated in Fig. 3 - Fig. 5, the cutting guard 3 comprises a first centre body 35 protruding from the top surface 33 inside the first cutting guard portion 31. Furthermore, as indicated in Fig. 3, Fig. 4, and Fig. 6, the cutting guard 3 comprises a second centre body 37 protruding from the top surface 33 inside the second cutting guard portion 32. The feature that the first and second centre bodies 35, 37 protrude from the top surface 33 means that each of the first and second centre bodies 35, 37 protrudes from the top surface 33 in a direction pointing towards a ground surface G when the cutting arrangement 2 is attached to a lawnmower 1 and the lawnmower 1 is positioned onto the ground surface G in the intended use position. As understood from the above described, this also means that each of the first and second centre bodies 35, 37 protrudes from the top surface 33 in a direction pointing towards the first plane P1 referred to above.

[0114] Radially outer delimiting surfaces 45 of the first centre body 35 are indicated in Fig. 5 and are schematically indicated in dashed lines in Fig. 3 and Fig. 4. Likewise, radially outer delimiting surfaces 47 of the second centre body 37 are indicated in Fig. 6 and are schematically indicated in dashed lines in Fig. 3 and Fig. 4. Moreover, as seen in Fig. 3 and Fig. 4, the delimiting wall 15 of the discharge opening 5 adjoins the first centre body 35 and the delimiting wall 17 of the discharge opening 5 adjoins the second centre body 37.

[0115] As is best seen in Fig. 5, according to the illustrated embodiments, the radially outer delimiting surfaces 45 of the first centre body 35 extends in directions Do substantially parallel to the first rotation axis ax1. Likewise, as is best seen in Fig. 6, the radially outer delimiting surfaces 47 of the second centre body 37 extends in directions Do’ substantially parallel to the second rotation axis ax2.

[0116] According to the illustrated embodiments, the height h45 of the radially outer delimiting surfaces 45 of the first centre body 35 is approximately 72% of the height h41 of the radially inner delimiting surfaces 41 of the first cutting guard portion 31. According to further embodiments, the height h45 of the radially outer delimiting surfaces 45 of the first centre body 35 may be at least 20%, or may be at least 50%, of the height h41 of the radially inner delimiting surfaces 41 of the first cutting guard portion 31.

[0117] Likewise, according to the illustrated embodiments, the height h47 of the radially outer delimiting surfaces 47 of the second centre body 37 is approximately 72% of the height h42 of the radially inner delimiting surfaces 42 of the second cutting guard portion 32. According to further embodiments, the height h47 of the radially outer delimiting surfaces 47 of the second centre body 37 may be at least 20%, or may be at least 50%, of the height h42 of the radially inner delimiting surfaces 42 of the second cutting guard portion 32.

[0118] Moreover, as is indicated in Fig. 3 and Fig. 4, according to the illustrated embodiments, the first centre body 35 is configured such that the distance d45 from the first rotation axis ax1 to radially outer delimiting surfaces 45 of the first centre body 35 decreases continuously, seen in the first rotational direction r1, within a third angle e3 having its vertex v1 at the first rotation axis ax1. Similarly, the second centre body 37 is configured such that the distance d47 from the second rotation axis ax2 to radially outer delimiting surfaces 47 of the second centre body 37 decreases continuously, seen in the second rotational direction r2, within a fourth angle e4 having its vertex v2 at the second rotation axis ax2.

[0119] According to the illustrated embodiments, each of the third and fourth angles e3, e4 is approximately 197 degrees. According to further embodiments, each of the third and fourth angles e3, e4 may exceed 90 degrees, or may exceed 180 degrees.

[0120] Due to these features, further improved aerodynamic properties are provided inside each of the first and second cutting guard portions 31, 32, as is further explained herein.

[0121] According to the illustrated embodiments, first cutting guard portion 31 is configured such that the volume of a space delimited by radially inner delimiting surfaces 41 of the first cutting guard portion 31 and the radially outer delimiting surfaces 45 of the first centre body 35 increases continuously within the full first angle e1 as seen in the first rotational direction r1. Likewise, second cutting guard portion 32 is configured such that the volume of a space delimited by radially inner delimiting surfaces 42 of the second cutting guard portion 32 and the radially outer delimiting surfaces 47 of the second centre body 37 increases continuously within the full second angle e2 as seen in the second rotational direction r2. The above mentioned features of the first and second cutting guard portions 31, 32 even further improve the aerodynamic properties inside the first and second cutting guard portions 31, 32 and facilitates generation of negative pressures inside the respective first and second cutting guard portions 31, 32in an energy efficient manner.

[0122] As indicated in Fig. 5 and Fig. 6, each of the first and second cutting units 11 , 12 comprises surfaces 21, 22 being angled relative to a rotation plane Pr1 , Pr2 of the cutting unit 11, 12 to generate an airflow in a direction dt transverse to the rotation plane Pr1 , Pr2 during rotation of the cutting unit 11, 12. In more detail, as indicated in Fig. 5 and Fig. 6, the surfaces 21 , 22 are angled relative to the rotation plane Pr1 , Pr2 to generate an airflow in a direction dt towards the top surface 33 of the cutting guard 3 during rotation of the first and second cuttings units 11 , 12 in the first and second rotational directions r1 , r2 respectively. In this manner, grass can be lifted in a direction towards the first and second cutting units 11, 12 respectively during rotation of the first and second cutting units 11, 12.

[0123] Moreover, due to the features of the cutting guard 3, including the first and second cutting guard portions 31, 32 thereof, relatively small angles between the surfaces 21, 22 and the rotation planes Pr1 , Pr2 can be utilized. By using relatively small angles between the surfaces 21, 22 and the rotation planes Pr1 , Pr2 of the first and second cutting units 11, 12, a low rotational resistance of the first and second cutting units 11, 12 is provided and hence also a low energy consumption of the cutting arrangement 2.

[0124] According to the illustrated embodiments, the angle between each surface 21, 22 and the respective rotation plane Pr1, Pr2 is approximately 15 degrees. According to further embodiments, the angle between each surface 21, 22 and the respective rotation plane Pr1, Pr2 may be within the range of 0 - 30 degrees, may be within the range of 2 - 25 degrees, or may be within the range of 10 - 20 degrees.

[0125] As indicated in Fig. 5 and Fig. 6, the surfaces 21 , 22 of the first and second cutting units 11 , 12, being angled relative to the rotation planes Pr1 , Pr2 of the first and second cutting units 11 , 12 respectively, are surfaces of the cutting members 61, 62. According to further embodiments, one or both of the first and second cutting units 11, 12 may comprise another type of assembly than a hub 51 , 52 and cutting members 61 ,62 pivotally attached thereto. For example, such an assembly may comprise a rigid cutting arm with cutting sections at radially outer portions of the cutting arm. In such embodiments, the surfaces 21, 22 of the first and second cutting units 11, 12 being angled relative to the rotation planes Pr1 , Pr2 of the first and second cutting units 11, 12, as referred to herein, may be surfaces of the rigid cutting arm.

[0126] According to the illustrated embodiments, the angle a1 between each of the first and the second rotation axes ax1, ax2 and the forward direction fd of the cutting arrangement 2 is approximately 87 degrees. According to further embodiments, the angle a1 between each of the first and the second rotation axes ax1, ax2 and the forward direction fd of the cutting arrangement 2 may be within the range of 78 - 102 degrees or may be within the range of 83 - 97 degrees. The angle a1 is indicated in Fig. 1, Fig. 5, and Fig. 6. The feature that the angle a1 between each of the first and the second rotation axes ax1 , ax2 and the forward direction fd of the cutting arrangement 2 is approximately 87 degrees means that the angle between each rotation plane Pr1 , Pr2 of the first and second cutting units 11, 12 and the first plane P1 indicated in Fig. 1 is approximately 3 degrees. In other words, according to the illustrated embodiments, the rotation planes Pr1 , Pr2 of the first and second cutting units 11, 12 are substantially parallel to the first plane P1 indicated in Fig. 1.

[0127] According to the illustrated embodiments, the width of the overlapping area A, as measured in directions coinciding with the line L in Fig. 3 and Fig. 4, is approximately 50 mm. According to further embodiments, the width of the overlapping area A, as measured in directions coinciding with the line L in Fig. 3 and Fig. 4, may be within the range of 5 - 100 mm, or may be within the range of 25 - 75 mm.

[0128] Moreover, according to the illustrated embodiments, the cutting width of the cutting members 61 , 62 of the first and second cutting units 11, 12 is approximately 50 mm. In other words, according to the illustrated embodiments, the cutting width of the cutting members 61, 62 of the first and second cutting units 11, 12 substantially corresponds to width of the overlapping area A, as measured in directions coinciding with the line L in Fig. 3 and Fig. 4. According to further embodiments, the cutting width of the cutting members 61, 62 of the first and second cutting units 11, 12 may be within the range of 15 - 100 mm, or may be within the range of 25 - 75 mm.

[0129] Moreover, according to the illustrated embodiments, the effective radius of each of the first and second cutting units 11, 12 is approximately 200 mm. According to further embodiments, the effective radius of each of the first and second cutting units 11 , 12 may be within the range of 100 - 300 mm, or may be within the range of 150 - 250 mm. The effective radius of each of the first and second cutting units 11 , 12 corresponds to the distance from the rotation axis ax1, ax2 of the cutting unit 11, 12 to the radially outer portion 1 T, 12’ of the cutting unit 11 , 12.

[0130] One or both of the control arrangements 23, 28 of the lawnmower 1 may comprise a computer which may take the form of substantially any suitable type of hardware or hardware / firmware device implemented using processing circuity such as, but not limited to, a processor, Central Processing Unit (CPU), a controller, an arithmetic logic unit (ALU), a digital signal processor, an Application Specific Integrated Circuit (ASIC), a circuit for digital signal processing (digital signal processor, DSP), a microcomputer, a field programmable gate array (FPGA), a System-on-Chip (SoC), a programmable logic unit, a microprocessor, an application-specific integrated circuit, or any other device capable of electronically performing operations in a defined manner, or other processing logic that may interpret and execute instructions. The herein utilised expression “computer” may represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above.

[0131] One or both of the control arrangements 23, 28 may further comprise a memory unit, wherein the computer may be connected to the memory unit, which may provide the computer with, for example, stored program code and / or stored data which the computer may need to enable it to do calculations. The computer may also be adapted to store partial or final results of calculations in the memory unit. The memory unit may comprise a physical device utilised to store data or programs, i.e. , sequences of instructions, on a temporary or permanent basis. According to some embodiments, the memory unit may comprise integrated 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 or non-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.

[0132] Moreover, one or both of the control arrangements 23, 28 of the lawnmower 1 may be connected to components of the lawnmower 1 for receiving and / or sending input and output signals. These input and output signals may comprise waveforms, pulses, or other attributes which the input signal receiving devices can detect as information and which can be converted to signals processable by the control arrangements 23, 28. These signals may then be supplied to the computer. One or more output signal sending devices may be arranged to convert calculation results from the computer to output signals for conveying to other parts of the control system of the lawnmower 1 and / or the component or components for which the signals are intended. Each of the connections to the respective components of the lawnmower 1 for receiving and sending input and output signals may take the form of one or more from among a cable, a data bus, a wireless connection, or the like.

[0133] In the embodiments illustrated, the lawnmower 1 comprises two control arrangements 23, 28. However, these might alternatively be implemented wholly or partly in one control arrangement or in more than two control arrangements.

[0134] It is to be understood that the foregoing is illustrative of various example embodiments and that the invention is defined only by the appended independent claims. A person skilled in the art will realize that the example embodiments may be modified, and that different features of the example embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the present invention, as defined by the appended independent claims.

[0135] As used herein, the term "comprising" or "comprises" is open-ended, and includes one or more stated features, elements, steps, components, or functions but does not preclude the presence or addition of one or more other features, elements, steps, components, functions, or groups thereof.

Claims

CLAIMS1. A cutting arrangement (2) configured to be attached to a lawnmower (1) such that a forward direction (fd) of the cutting arrangement (2) coincides with a forward direction (fd’) of the lawnmower (1), wherein the cutting arrangement (2) comprises: a cutting guard (3), and a first cutting unit (11) configured to rotate in a first rotational direction (r1) around a first rotation axis (ax1) such that one or more radially outer portions (11’) of the first cutting unit (11) orbits in a first circular path (c1) inside the cutting guard (3), a second cutting unit (12) configured to rotate in a second rotational direction (r2) around a second rotation axis (ax2) such that one or more radially outer portions (12’) of the second cutting unit (12) orbits in a second circular path (c2) inside the cutting guard (3), wherein the second rotational direction (r2) is opposite to the first rotational direction (r1), and wherein the second circular path (c2) overlaps the first circular path (c1) such that an overlapping area (A) is formed between the first and second circular paths (c1, c2), and wherein the cutting guard (3) comprises a discharge opening (5) arranged to eject clippings along a main discharge direction (md) from the cutting guard (3), wherein a tangential movement direction (T 1 , T2) of the first and second cutting units (11, 12) coincides with the main discharge direction (md) at a location within the overlapping area (A) upon rotation of the first and second cutting units (11 , 12) around the respective first and second rotation axes (ax1, ax2).

2. The cutting arrangement (2) according to claim 1 , wherein the angle (a1) between each of the first and the second rotation axes (ax1 , ax2) and the forward direction (fd) of the cutting arrangement (2) is within the range of 78 - 102 degrees, or is within the range of 83 - 97 degrees.

3. The cutting arrangement (2) according to claim 1 or 2, wherein the cutting arrangement (2) is configured such that the angle (a2) between the forward direction (fd) of the cutting arrangement (2) and a line (L) passing through each of the first and second rotation axes (ax1, ax2) is within the range of 75 - 105 degrees, or is within the range of 85 - 95 degrees.

4. The cutting arrangement (2) according to any one of the preceding claims, wherein the discharge opening (5) is arranged at a rear portion (3’) of the cutting guard (3) as seen relative to the forward direction (fd) of the cutting arrangement (2).

5. The cutting arrangement (2) according to any one of the preceding claims, wherein the discharge opening (5) is funnel-shaped with an increasing width (w) along the main discharge direction (md).

6. The cutting arrangement (2) according to any one of the preceding claims, wherein the discharge opening (5) comprises two opposing delimiting walls (15, 17), and wherein the angle (a3) between the forward direction (fd) of the cutting arrangement (2) and each of the two opposing delimiting walls (15, 17) is within the range of 5 - 23 degrees, or is within the range of 10 - 18 degrees.

7. The cutting arrangement (2) according to any one of the preceding claims, wherein the angle (a4) between the main discharge direction (md) and the forward direction (fd) of the cutting arrangement (2) is within the range of 155 - 205 degrees, or is within the range of 175 - 185 degrees.

8. The cutting arrangement (2) according to any one of the preceding claims, wherein the angle between the first and second rotation axis (ax2) is less than 10 degrees, or is less than 5 degrees.

9. The cutting arrangement (2) according to any one of the preceding claims, wherein the cutting guard (3) comprises a first cutting guard portion (31) enclosing part of the first circular path (c1) and a second cutting guard portion (32) enclosing part of the second circular path (c2).

10. The cutting arrangement (2) according to claim 9, wherein the cutting guard (3) is configured such that the distance (d1 , dT) between each of the first and second circular paths (c1 , c2) and a front section (3T, 32’) of the first and second cutting guard portions (31, 32) respectively is greater than the distance (d2, d2’) between each of the first and second circular paths (c1, c2) and a rear section (31”, 32”) of the first and second cutting guard portions (31 , 32) respectively.

11. The cutting arrangement (2) according to claim 9 or 10, wherein the first cutting guard portion (31) is configured such that the distance (d41) between the first rotation axis(ax1) and radially inner delimiting surfaces (41) of the first cutting guard portion (31) increases continuously, seen in the first rotational direction (r1), within a first angle (e1) having its vertex (v1) at the first rotation axis (ax1), and wherein the first angle (e1) exceeds 90 degrees, or exceeds 180 degrees, wherein the second cutting guard portion (32) is configured such that the distance (d42) between the second rotation axis (ax2) and radially inner delimiting surfaces (42) of the second cutting guard portion (32) increases continuously, seen in the second rotational direction (r2), within a second angle (e2) having its vertex (v2) at the second rotation axis (ax2), and wherein the second angle (e2) exceeds 90 degrees, or exceeds 180 degrees.

12. The cutting arrangement (2) according to any one of the claims 9 - 11, wherein the radially inner delimiting surfaces (41) of the first cutting guard portion (31) extend in directions (Di) substantially parallel to the first rotation axis (ax1), and wherein the radially inner delimiting surfaces (42) of the second cutting guard portion (32) extend in directions (Di’) substantially parallel to the second rotation axis (ax2).

13. The cutting arrangement (2) according to any one of the claims 9 - 12, wherein the cutting guard (3) comprises a top surface (33), a first centre body (35) protruding from the top surface (33) inside the first cutting guard portion (31), and a second centre body (37) protruding from the top surface (33) inside the second cutting guard portion (32).

14. The cutting arrangement (2) according to claim 13, wherein radially outer delimiting surfaces (45) of the first centre body (35) extends in directions (Do) substantially parallel to the first rotation axis (ax1), and wherein radially outer delimiting surfaces (47) of the second centre body (37) extends in directions (Do’) substantially parallel to the second rotation axis (ax2).

15. The cutting according to claim 13 or 14, wherein the height (h45) of the radially outer delimiting surfaces (45) of the first centre body (35) is at least 20%, or is at least 50%, of the height (h41) of the radially inner delimiting surfaces (41) of the first cutting guard portion (31), and wherein the height (h47) of the radially outer delimiting surfaces (47) of the second centre body (37) is at least 20%, or is at least 50%, of the height (h42) of the radially inner delimiting surfaces (42) of the second cutting guard portion (32).

16. The cutting arrangement (2) according to any one of the claims 13 - 15, wherein the first centre body (35) is configured such that the distance (d45) from the first rotation axis(ax1) to radially outer delimiting surfaces (45) of the first centre body (35) decreases continuously, seen in the first rotational direction (r1), within a third angle (e3) having its vertex (v1) at the first rotation axis (ax1), and wherein the third angle (e3) exceeds 90 degrees, or exceeds 180 degrees, and wherein the second centre body (37) is configured such that the distance (d47) from the second rotation axis (ax2) to radially outer delimiting surfaces (47) of the second centre body (37) decreases continuously, seen in the second rotational direction (r2), within a fourth angle (e4) having its vertex (v2) at the second rotation axis (ax2), and wherein the fourth angle (e4) exceeds 90 degrees, or exceeds 180 degrees.

17. The cutting arrangement (2) according to any one of the claims 13 - 16, wherein the discharge opening (5) comprises two opposing delimiting walls (15, 17) each adjoining one of the first and second centre bodies (35, 37).

18. The cutting arrangement (2) according to any one of the preceding claims, wherein the cutting arrangement (2) comprises a motor assembly (7) configured to rotate the first and second cutting units (11 , 12) at synchronized rotational speeds.

19. The cutting arrangement (2) according to claim 18, wherein the motor assembly (7) comprises a first electric motor (ml) configured to rotate the first cutting unit (11), a second electric motor (m2) configured to rotate the second cutting unit (12), and a control arrangement (23) configured to operate the first and second electric motors (ml, m2) at synchronized rotational speeds.

20. The cutting arrangement (2) according to any one of the preceding claims, wherein each of the first and second cutting units (11 , 12) comprises one or more surfaces (21, 22) being angled relative to a rotation plane (Pr1, Pr2) of the cutting unit (11 , 12) to generate an airflow in a direction (dt) transverse to the rotation plane (Pr1 , Pr2) during rotation of the cutting unit (11 , 12).

21. The cutting arrangement (2) according to claim 20, wherein the surfaces (21, 22) are angled relative to the rotation plane (Pr1 , Pr2) to generate an airflow in a direction (dt) towards the top surface (33) of the cutting guard (3) during rotation of the first and second cuttings units (11, 12) in the first and second rotational directions (r1 , r2) respectively.

22. The cutting arrangement (2) according to any one of the preceding claims, wherein each of the first and second cutting units (11 , 12) comprises a hub (51 , 52) and a number of cutting members (61, 62) pivotally attached at a periphery of the hub (51, 52).

23. The cutting arrangement (2) according to claim 20 or 21 and claim 22, wherein the one or more surfaces (21 , 22) are surfaces of the cutting members (61 , 62).

24. A lawnmower (1) comprising a cutting arrangement (2) according to any one of the preceding claims.

25. The lawnmower (1) according to claim 24, wherein the lawnmower (1) is a self-propelled robotic lawnmower configured to navigate and cut grass in an area in an autonomous manner.

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