Improvements in lawn mowers

Abstract: A lawn mower comprises a cutting unit consisting of two rotors (17) coupled together within a single casing (14) to rotate in opposite directions, they carrying at least two aligned blades (18), the distance between the axes of the rotors (17) being such that the areas covered by the blades (18) when rotating are partially superposed in correspondence with that axis of symmetry of the pair of rotors which coincides with the mower axis, the direction of rotation of the two rotors (17) being such that the direction of movement of the blades (18) when in proximity to said axis of symmetry is the same as the forward travel direction of the mower.

Description: This patent relates to self-propelled lawn mowers for parks or gardens, of the type comprising a cutting unit consisting of two rotors coupled together within a single casing to rotate in opposite directions, each carrying at least two equidistant blades. The casing is open lowerly and matches the shape of the areas covered by said blades, these being partially superposed in the central region to convey the grass, in the opposite direction to the travel direction, into a suction-evacuation duct which feeds it into a collection bin mounted to the rear of the mower. Mowers of this type have gradually assumed increasing dimensions and working power, with the result that certain operating defects have appeared which it is the purpose of the present invention to obviate. A first drawback arises from the fact that the cut grass, which itself is moist and sticky, tends to adhere to the walls of the casing to form groups which, besides hindering proper mower operation, become suddenly detached on account of their own weight when they reach a certain size, to fall onto the ground without being drawn in and conveyed to the collection bin. Said groups form both at the mouth of the evacuation duct leading to the bin, and on the upper part of the casing enclosing the blades. In this respect, these are shaped as the blades of a propeller generating an upwardly directed air stream, and although on the one hand this favours the straightening of the stalks to facilitate their cutting, on the other hand it propels the grass towards the upper surface of the casing, causing it to undesirably accumulate. The presence of said groups also hinders correct intake of the grass gradually cut off, causing this to deposit irregularly on the ground. In addition the direction of rotation of the blades concentrates the grass flow between the two rotors, which further aggravates the aforesaid problems. Furthermore, they are even more apparent if operating on grass of a certain height, because the product volume increases. Again, in the case of tall grass, the front edge of the casing enclosing the blades, and which is lower than these latter, bends forward the grass to be cut, so that its stalks escape the action of the rotary blades, especially in the central region of the mower, resulting in irregularly cut grass. US-A-5214906 discloses a lawn mower comprising a cutting unit consisting of two rotors coupled together within a single casing to rotate in opposite directions, they carrying at least two aligned blades, the distance between the axes of the rotors beign such that the areas covered by the blades when rotating are partially superposed in correspondence with the axis of symmetry of the pair of rotors which coincides with the mower axis, the direction of rotation of the two rotors being such that the direction of movement of the blades when in proximity to said axis of symmetry is the same as the forward travel direction of the mower. According to US-A-5214906 the mass of cut grass is conveyed to the outside of the two rotors in correspondence with the lateral regions of the casing, and escapes tangentially to prevent formation of the unwanted accumulations in the central region in correspondence with the evacuation duct. Nevertheless formation of cut grass accumulations occur on the upper wall of the casing, and hinder the proper mower operation. Formation of cut grass accumulations on the upper wall of the casing is prevented, according to the invention, by providing a second-blade overlying and spaced from each blade, to halt the upward flow of the cut grass and to discharge it by centrifugal force. Finally, according to the invention, the central front region of the blade-enclosing casing is provided with a small swinging flap which rises automatically when particularly tall grass is to be cut. In this manner the grass lying between the rotor axes is not bent. According to a preferred embodiment of the invention, to the mouth of the evacuation duct there is applied a bladed impeller which facilitates the conveying of the grass into the duct. The impeller axis is preferably horizontal, perpendicular to the travel direction, the impeller blades being radial. Besides facilitating the flow of cut grass into the evacuation duct, the presence of the impeller enables the longitudinal dimensions of the mower to be reduced in that it enables the blade-containing casing to be shaped with its rear edge practically perpendicular to the travel direction. The merits and operational and constructional characteristics of the invention will be apparent from the detailed description given hereinafter with reference to the figures of the accompanying drawings, which show a preferred embodiment thereof by way of non-limiting example. Figure 1 is a schematic perspective view of an improved lawn mower according to the invention. Figure 2 is a view of the cutting unit taken from above. Figure 3 is a section on the line III-III of Figure 2. Figure 4 is a section on the line IV-IV of Figure 2. Figure 5 is a partial schematic section through Figure 1. Figure 6 is a view of the cutting unit taken from below. Figure 7 shows a second embodiment of the invention in a view similar to Figure 5. Figure 8 is a view from above of the cutting unit of the second embodiment of the invention. Figure 9 is a section on the line IX-IX of Figure 8. Figure 10 is a section on the line ¦X-X of Figure 8. The figures show the lawn mower 1, which comprises a main frame 2 provided with two independent drive wheels 3 and two rear swivel wheels 4, of which only one is visible. On the frame 2 there are provided a hydraulic power unit 5 operated by an internal combustion engine, a tiltable collection bin 6 and a driving seat 7 with the respective controls, all in a well-known usual form so that more detailed description is not required. In front of the drive wheels 3 there is hinged a secondary frame supporting the cutting unit 9. Said secondary frame can be raised into the rest position and lowered into the working position, and comprises two parallel arms 10 provided at their ends with two swivel wheels 11. The arms 10 each comprise two holes 12 for receiving two vertical pins 13 extending from the top of a casing 14. The pins 13 (Figures 3, 4) are provided with holes 15 which enable the casing 14 to be fixed to the arms 10 at the desired working height. To facilitate its positioning the casing 14 is provided with upper handles 16. The casing 14 is positioned symmetrically about the mower axis, and supports two rotors 17 (Figures 3, 6), each provided with two aligned blades 18. The two rotors are connected to a single operating unit 19, of usual type, positioned above the casing 14. The pair of blades of one rotor is offset by 90° from the pair of blades of the other rotor, the distance between the axes of rotation of the two rotors being such that the areas covered by the pairs of blades are partly superposed in correspondence with the longitudinal axis of the mower. The two rotors move in opposite directions, their directions being such that the blades move, when at the centre of the mower, in the same direction as the forward travel direction of the mower. A second-blade 188 overlies each blade 18, which comprises a cutting edge 181 and a fin 182 bent upwards to give the blade the behaviour of a fan blade. A fin, not shown, analogous to the fin 182 but directed downwards, can be provided at the end of the second-blade. As can be seen from the figures, the casing 14 largely matches the area covered by the blades, it having a front edge 20 substantially perpendicular to the travel direction, and a rear edge 21 connected tangentially to the area covered by the blades and converging into an evacuation duct 22 for the cut grass. According to the invention the central part of the front edge 20 is occupied by a door or flap 23 which is raised automatically towards the casing interior when particularly tall grass is cut. The evacuation duct 22 is connected by a flexible pipe 24 to the suction duct of a fan 25 (Figure 5) located on the main frame 2 of the mower. When the cut grass bin 6 is lowered, the delivery duct of the fan 25 opens into a vertical duct 27 rigid with said bin and conveying the cut grass into it. Figures 7 to 10 show a second embodiment of the invention, in these latter figures the same reference numerals having been used for the same elements already shown in Figures 1 to 6. In said second embodiment the rear edge 210 of the casing 14 is substantially perpendicular to the mower axis and converges at its centre into a cowling 211 containing an impeller 212. The axle 213 of the impeller carries a pulley 214 which is connected by a transmission belt 215 to the drive pulley 216 keyed onto the horizontal shaft 217 of the operating unit 19 for the rotors 17. The impeller 212 is composed of two coaxial groups of four mutually perpendicular impeller blades, the blades of one group being offset by 45° from the blades of the other group. At its rear the cowling 211 is connected to the evacuation duct 22.

Claims: A lawn mower comprising a cutting unit consisting of two rotors (17) coupled together within a single casing (14) to rotate in opposite directions, carrying at least two aligned blades (18), the distance between the axes of the rotors being such that the areas covered by the blades when rotating are partially superposed in correspondence with that axis of symmetry of the pair of rotors which coincide with the mower axis, the direction of rotation of the two rotors (17) being such that the direction of movement of the blades (18) when in proximity to said axis of symmetry is the same as the forward travel direction of the mower, characterised in that a second blade (188) overlies and overlaps each of the blades (18) fixed to the rotors. A lawn mover according to the claim 1 characterized in that said second blade (188) comprises a fin directed downwards to give the blade the behaviour of a fan blade. A lawn mower as claimed in claim 1, characterised in that the casing (14) enclosing the rotors has its front portion in the direction of travel provided with a liftable door or flap (23) which oscillates automatically towards the casing interior responsive to the grass thrust. A mower as claimed in the preceding claims, characterised in that at the centre of the rear edge (21, 210) of the casing (14) enclosing the rotors (17) carrying the cutting blades there is located an impeller (212) which has its axis (213) horizontal and perpendicular to the travel direction and is enclosed in a cowling (211) which connects to the evacuation duct (22), the direction of rotation of said impeller being the same of that of the mower wheels.

Inventors: FERRARI GIANNI, FERRARI, GIANNI
Applicants: GIANNI FERRARI S R L, GIANNI FERRARI S.R.L.
Application year: 1996
Main classification: A01D34
IPC codes: A01D43, A01D34