Device for fastening a drive unit to a lawn-mower body

Abstract: Device for fastening a drive unit (4) to a body (1) of lawn-mower, said drive unit comprising a pulley (5) which receives a transmission belt (3) of an engine (2) and a transmission shaft (6) in order to actuate a pair of wheels (9). The device comprises a tie rod (11) hinged to the drive unit at one end, and elastic stress means (12, 13, 14, 15) coupled to a second end of said tie rod for tensioning said belt, said elastic means being arranged in such a way as to develop an elastic force (F1) lying on a same plane in which a tension developed by the belt (3) also lies, so that said elastic force has the same direction, the same intensity but opposite sense with respect to the tension exerted by the belt on the drive unit.

Description: The present invention refers to a device for fastening a drive unit to a lawn-mower body. In the field of lawn-mowers, by drive unit, or transmission unit, it is meant the assembly of the mechanical parts which provides to transmit the motive power of an engine, generally transmitted by means of a belt, to a transmission shaft that operates a pair of wheels. The transmission shaft rest on the body on two points by means of bushings or bearings, and is provided with gears that operate the wheels at both ends. The currently known solutions for fastening the drive unit to the body, which employ screws, or springs, or screws combined with springs, produce a stress on the transmission shaft, stress that is more or less elevated as a function of the tension load of the belt, of the position of the drive unit with respect to the two bearing points of the transmission shaft onto the body, and of the position of the drive group fastening point onto the body with respect to the tension point of the belt. The stress on the transmission shaft determines its deflexion, with the consequence that there is a greater wear both of the transmission shaft, where this rests on the drive unit, and on the shaft bushings or bearings onto the body. If the stress is of a certain consistency, case that occurs for example during take-off from the lawn-mower standstill condition, the transmission shaft can even break. In order to obviate these problems, the transmission shaft could be overdimensioned, but this would determine an increase in costs and in volumes. In view of the state of the art described above, object of the present invention is to provide for a device for fastening the drive unit to the body which allows substantially to eliminate the stresses on the transmission shaft. According to the present invention, such object is attained by means of a device for fastening a drive unit to a lawn-mower body, said drive unit comprising a pulley which receives an engine transmission belt and a transmission shaft in order to actuate a pair of wheels, characterised in that it comprises a tie rod hinged to the drive unit at one end, and elastic stress means coupled to the other end of said tie rod for tensioning said belt, said elastic means being arranged in such a way as to develop an elastic force lying on a same plane in which a tension developed by the belt lies, said elastic force having the same direction, the same intensity but opposite sense with respect to the tension exerted by the belt on the drive unit. The characteristics and the advantages of the present invention will be rendered more evident by the following detailed description of its embodiment, illustrated as a non-restrictive example in the enclosed drawings, where: Figure 1 is a simplified section view, according to a vertical mid plane, of a lawn-mower, which brings out the drive unit and the fastening device according to the present invention; Figure 2 is a top plan view of the lawn-mower of Figure 1. With reference to the drawings, in Figure 1 a lawn-mower is shown schematically in section according to a longitudinal vertical plane. In the figure, 1 indicates a body of lawn-mower. There is shown a driving shaft 2 that, by means of a pulley and of a transmission belt 3, transmits motion to a drive unit 4. The drive unit 4 comprises in a known way a pulley 5 that receives the transmission belt 3, and a mechanical parts assembly (that can comprise also a multiple shift gear box) for transmitting motion to a transversal transmission shaft 6. As it can be seen in Figure 2, the transmission shaft 6 rests on two points 7, 8 of the body 1 by means of bushings or bearings, and is provided in a known manner with gears that actuate the wheels 9 at its two ends. On the upper part of the crankcase of the drive unit 4 a tie rod 11 is hinged. A final portion of the tie rod 11 lies on the same plane on which the rim of the pulley 5 lies, and is threaded at the end. The final portion of the tie rod 11 lying on the aforementioned plane passes through a hole made into a sleeve 12, around the tie rod 11 there is an helical spring 13 that on one side abuts against the bottom of the sleeve 12, while on the other is kept compressed by a washer 14 whose position along the tie rod axis 11 can be adjusted by means of a nut 15 screwed on the threaded end of the final portion of the tie rod itself. The washer 14 has greater dimensions than the sleeve, in such a way as to create a stroke end for the compression of the spring when the washer 14 abuts against the edge 16 of the sleeve 12. The elastic reaction of the spring 13 provides the necessary force to tension the belt 3. Thanks to the fact that the elastic reaction force of the spring 13 lies along the same plane on which there lies the tension exerted by the belt 3 on the drive unit, the reaction force of the spring 13 has the same direction, the same intensity but opposite sense with respect to the tension exerted by the belt 3 (vectors F1 and F2 in Figure 1). In this way, the resultant of the two forces is null, therefore the transmission shaft 6 is not subject to deflexion. Working on the nut 15, it is possible to increase or to decrease the elastic reaction force of the spring 13, in such a way as to increase or to decrease correspondingly the tension of the belt 3. In addition, a certain distance between the washer 14 and the edge 16 of the sleeve 12 allows to control the correct tension to be applied to the belt during the mounting step, independently from the tolerances of the pitch development of the belt. In addition, the arrest of the washer 14 against the edge 16 of the sleeve 12 prevents that, in condition of burdensome initial take-off, the belt 3 comes out of the pulley 5.

Claims: Fastening device of a drive unit (4) to a body (1) of lawn-mower, said drive unit comprising a pulley (5) which receives an engine transmission belt (3) and a transmission shaft (6) in order to actuate a pair of wheels (9), characterised in that it comprises a tie rod (11) hinged to the drive unit at one end, and elastic stress means (12, 13, 14, 15) coupled to the other end of said tie rod for tensioning said belt, said elastic means being arranged in such a way as to develop an elastic force (Fl) lying on a same plane in which a tension developed by the belt (3) lies, said elastic force having the same direction, the same intensity but opposite sense with respect to the tension exerted by the belt on the drive unit. Fastening device according to claim 1, characterised in that said tie rod (11) comprises at least one tie rod portion lying on said plane, said elastic stress means (12, 13, 14, 15) comprising an helical spring (13) inserted on said tie rod portion and that on one side reacts against the body (1) and on the other co-operates with abutment means (14, 15) integral with said portion of the tie rod. Fastening device according to claim 2, characterised in that said abutment means (14, 15) are adjustable in position along the axis of said tie rod portion in order to vary the amount of tension of the belt (3). Fastening device according to claim 3, characterised in that said abutment means (14, 15) comprise a washer (14) inserted on said tie rod portion and a nut (15) screwed on said tie rod portion. Fastening device according to claim 4, characterised in that it comprises stroke end means (16) of said abutment means (14, 15) for stopping upon take-off the advancement of the drive unit and therefore preventing the belt 3 from coming out of the pulley 5.

Inventors: FERRARI MAURIZIO, FERRARI, MAURIZIO
Applicants: CASTELGARDEN SPA, CASTELGARDEN S.P.A.
Application year: 1997
Main classification: A01D34
IPC codes: F16H7, A01D34