TWO DRIVEN SHAFTS

The present invention relates to a mechanical transmission device, and in particular to a mechanical device which can transmit a torque from a drive shaft to two driven shafts.

European patent 1623217 discloses a device suitable for transmitting a torque from a drive shaft to a driven shaft, wherein the drive shaft is mechanically connected to a first engagement rotor which can be mechanically coupled or uncoupled with a second engagement rotor mechanically connected to the driven shaft and coaxially arranged around the first engagement rotor, by extracting or retracting, respectively, at least one mobile tooth which can rotate in a seat made in the first engagement rotor, a driving rotor being coaxially and rotatably arranged around the first engagement rotor and being provided with braking means, so that the relative rotation of the driving rotor with respect to the first engagement rotor causes the extension or the retraction of the mobile tooth according to the direction of this relative rotation.

When said device is applied to a motorized vehicle, for example a lawnmower, a differential must be connected between the driven shaft and the axles of the wheels for allowing a relative rotation between the latter when the device is engaged. It is therefore an object of the present invention to provide a device free from said disadvantages, namely a device which allows to transmit a torque directly from the drive shaft to the wheels without a differential and anyway with the possibility of a relative rotation between the wheels. Said object is achieved with a device, whose main features are disclosed in the first claim, while other features are disclosed in the remaining claims.

Thanks to the doubling with adaptation of the components, as well as their particular arrangement with respect to the wheel connected to the drive shaft, the device according to the present invention allows not only the automatic and independent engagement and disengagement of two driven shafts, as in said known device, but also the relative rotation between these shafts, so as to not require the connection to a differential when it is applied to a motorized vehicle. For reducing the dimensions and improving the reliability of the device according to the present invention, the driven shafts are preferably connected to each other by a coaxial pin which allows the mutual rotation of these shafts and the wheel is preferably provided with a plurality of longitudinal holes in which longitudinal pins are inserted, so that one or both ends of these pins protrude from both sides of the wheel and are inserted in longitudinal holes made in the first engagement rotors.

For improving the automatic engagement and disengagement of the device according to the present invention, the driving rotors are preferably provided with longitudinal openings crossed by said longitudinal pins, so as to allow a limited relative rotation between the wheel and the driving rotors. For the same purpose, the braking means preferably comprise a spring formed by a curved metal wire arranged in a circular groove made around the driving rotors, wherein the ends of the spring are bent outwards and can freely rotate along a circle arc with respect to the container which contains the first engagement rotors, the second engagement rotors and the driving rotors.

Further advantages and features of the device according to the present invention will become clear to those skilled in the art from the following detailed and non-limiting description of an embodiment thereof with reference to the attached drawings, wherein: figure 1 shows a perspective view of the disengaged device; - figure 2 shows a perspective view of the device of figure 1 , without cover and pulley; figure 3 shows a top view of the device of figure 2; figure 4 shows section IV-IV of figure 3; figure 5 shows section V-V of figure 3; - figure 6 shows section VI-VI of figure 3; figure 7 shows section VII-VII of figure 3; figure 8 shows section VIII-VIII of figure 3; and figures 9 to 12 correspond to figures 5 to 8, but with the engaged device.

Referring to figures 1 to 8, it is seen that the transmission device according to the present invention comprises in a known way a container 1 which is closed by an upper cover 2 by means of a plurality of screws (not shown) inserted in corresponding seats 3 arranged along the upper edges of container 1. The container has a substantially prismatic shape, wherein the front wall Ia is perpendicular to two side walls Ib and rear wall Ic is curved outward. Cover 2 is provided with a hole in which a drive shaft 4 keyed to a transmission device, for example a pulley 5, is inserted for the connection to a motor.

Two driven shafts 6, 6' are arranged in a substantially perpendicular manner to drive shaft 4, so that they both cross a side wall Ib of container 1. A worm screw 7 mechanically coupled with a wheel 8, in particular a cogwheel provided with an axial hole in which at least one end of driven shafts 6, 6' is rotatably arranged, is integral with drive shaft 4, which is rotatably supported in container 1 by a bearing 9. Cogwheel 8 is thus mechanically connected to drive shaft 4, while driven shafts 6, 6' are mutually connected by a coaxial pin 10 which allows the mutual rotation of these shafts 6, 6'. Cover 2 is provided with another bearing (not visible in the figures) for rotatably supporting drive shaft 4. Worm screw 7 is arranged at least partially in the curvature of rear wall 1 c of container 1. Cogwheel 8 is provided with a plurality of longitudinal holes in which longitudinal pins 11 are inserted, in particular three longitudinal pins which cross cogwheel 8, so that one or both ends of longitudinal pins 11 protrude from both ends of cogwheel 8. Longitudinal pins 11 are in turn inserted in longitudinal holes made in first engagement rotors 12, 12' coaxially arranged beside cogwheel 8, so that cogwheel 8 is located between these rotors 12, 12' and can rotate together with them. First engagement rotors 12, 12' are provided with an axial hole in which a driven shaft 6, 6' is rotatably arranged. First engagement rotors 12, 12' can be mechanically coupled or uncoupled with second engagement rotors 13, 13', coaxially arranged beside first engagement rotors 12, 12', by extracting or retracting, respectively, at least one mobile tooth 14 which can rotate in a seat made in first engagement rotors 12, 12', in particular close to their outer surface. Second engagement rotors 13, 13' are provided with an axial hole so that each driven shaft 6, 6' is keyed to a second engagement rotor 13, 13' by means of a transversal pin 15, 15'. Mobile tooth 14 of first engagement rotors 12, 12' is urged into its retracted position by elastic means 16, in particular by a spring formed by a curved metal wire arranged around first engagement rotors 12, 12'. An end of spring 16 urges mobile tooth 14 into its seat, while the other end is locked with respect to first engagement rotors 12, 12', for example is bent into a radial seat 17, 17' made therein. Driving rotors 18, 18' are coaxially and rotatably arranged around driven shafts 6, 6' between cogwheel 8 and first engagement rotors 12, 12'. Driving rotors 18, 18' are provided with braking means, which in the present embodiment comprise a spring 19, 19' formed by a curved metal wire arranged in a circular groove made around driving rotors 18, 18'. The ends 20, 20' of springs 19, 19' are bent outwards, so that they can abut against a member integral with container 1 or cover 2 for opposing a friction to the rotation of driving rotors 18, 18' with respect to container 1. Driving rotors 18, 18' are provided with longitudinal openings 21 crossed by longitudinal pins 11, so as to allow a relative rotation limited to about 20° between cogwheel 8 and driving rotors 18, 18'. Mobile tooth 14 of first engagement rotors 12, 12' is provided with a cursor 22 suitable for sliding in a groove 23 made in driving rotors 18, 18', so that the relative rotation of driving rotors 18, 18' with respect to first engagement rotors 12, 12' causes the extension or the retraction of mobile tooth 14 according to the direction of this relative rotation. Figures 7 and 8 show mobile tooth 14 in the retracted position, namely with drive shaft 4 mechanically uncoupled with driven shaft 6. This condition occurs when drive shaft 4 is not rotated by external means, for example by a motor, so that cogwheel 8, first engagement rotors 12, 12' and driving rotors 18, 18' are still, while driven shafts 6, 6' and second engagement rotors 13, 13' can freely rotate in both directions, since second engagement rotors 13, 13' are mechanically uncoupled with first engagement rotors 12, IT.

Referring also to figures 9 to 12, it is seen that when drive shaft 4 is rotated, for example by a motor, in a determinate direction, the rotation of drive shaft 4 is transmitted to first engagement rotors 12, 12' through worm screw 7 and cogwheel 8. Driving rotors 18, 18', braked by springs 19, 19' having ends 20, 20' which come into contact with container 1, rotate with respect to first engagement rotors 12, 12', so that mobile tooth 14 of first engagement rotors 12, 12' is extracted by the movement of the cursor in the groove of driving rotors 18, 18'. When mobile tooth 14 has been completely extracted, thereby rotating with first engagement rotors 12, 12', it abuts against at least one protrusion 24 projecting inside a cavity 25 made in second engagement rotors 13, 13' around first engagement rotors 12, 12', so that driven shafts 6, 6' are rotated by second engagement rotors 13, 13' mechanically coupled with first engagement rotors 12, 12' by means of mobile tooth 14 extracted by first engagement rotors 12, 12'.

When drive 5 stops, spring 16 urges mobile tooth 14 into its seat of first engagement rotors 12, 12', thereby slightly rotating driving rotors 18, 18' with respect to first engagement rotors 12, 12' and overcoming the friction opposed by springs 19,

19' to this relative rotation. If drive shaft 4 rotates in the inverse direction, the relative rotation of first engagement rotors 12, 12' with respect to driving rotors 18, 18' causes the retraction of mobile tooth 14 into its seat. The ends 20, 20' of springs 19, 19' can move along a circle arc of about 20° between container 1 and cover 2, so that engagement rotors 18, 18' can freely rotate along said arc with respect to container 1.

Possible modifications and/or additions may be made by those skilled in the art to the hereinabove disclosed and illustrated embodiment while remaining within the scope of the following claims.