The present invention refers to a system for synchronising the operation of at least two actuators, in particular for trucks for transporting motor vehicles and trailers. On ^' known trailers, one of the normally used systems for lifting the upper platforms is composed of two sliding guides, one on each side of the vehicle, in which the platform support can linearly move on ^' a vertical axis. Such support can be moved by a kinematism of the "worm screw - nut screw" type. In order to keep the platform horizontal, in a transverse plane, the two right and left "worm screw - nut screw" kinematisms must synchronously move, otherwise the platform can get slanted on one side, generating a load anomaly, in addition to an aesthetic defect. Such synchronism is normally guaranteed by the fact that the motion is provided by a single orbital motor, divided and kept synchronous by a mechanical interconnection between the two screws, performed through angular transmissions, joints, shafts and sleeves. These devices create an encumbrance that could be exploited to lower the vehicle load, at the same time imposing a high construction cost, a design constraint for housing the various components, a non-neglectable weight and important maintenance operations .

Therefore, object of the present invention is solving the above prior art problems, by providing a system for synchronising the operation of at least two actuators, in particular for trucks for transporting motor vehicles and trailers, free of mechanical interconnecting means between the two screws necessary for synchronising the motors in prior art systems .

Another object of the present invention is providing a system for synchronising the operation of at least two actuators, in particular for trucks for transporting motor vehicles and trailers, that is less encumbrant, less costly, lighter and more reliable than prior art synchronising systems.

The above and other objects and advantages of the invention, as will result from the following description, are obtained with a system for synchronising the operation of at least two actuators as described in Claim 1. Preferred embodiments and non-trivial variations of the present invention are the subject matter of the dependent claims. It will be immediately obvious that numerous variations and modifications (for example related to shape, sizes, arrangements and parts with equivalent functionality) can be made to what is described, without departing from the scope of the invention, as claimed in the dependent claims.

The present invention will be better described by some preferred embodiments thereof, provided as a non-limiting example, with reference to the enclosed drawings, in which: - FIG. 1 shows a block diagram of a preferred embodiment of the system for synchronising the operation of at least two actuators according to the present invention;

FIG. 2 shows the block diagram of the system of FIG. 1 in a first synchronising mode thereof;

FIG. 3 shows the block diagram of the system of FIG. 1 in a second synchronising mode thereof;

FIG. 4 shows a block diagram of another preferred embodiment of the system for synchronising the operation of at least two hydraulic motors according to the present invention;

FIG. 5 shows the block diagram of the system of FIG. 4 in a first synchronising mode thereof; and

FIG. 6 shows the block diagram of the system of FIG. 4 in a second synchronising mode thereof.

With reference to the Figures, it is possible to note that the synchronising system 1 comprises at least one first and one second actuator, at least first detection means Rl and at least second detection means R2, such detection means Rl, R2 cooperating with control and management means C, preferably made as at least one electronic unit, in order to directly or indirectly detect possible differences in angular displacement between the first actuator and the second actuator, such first and second actuators being fed by at least one hydraulic feeding circuit L comprising at least one first by-pass line Bl of the first actuator, connected with the hydraulic feeding circuit L, upstream of such first actuator, by interposing first switching means between such first by-pass line Bl and such hydraulic feeding circuit L, and at least one second by-pass line B2 of the second actuator, connected with the hydraulic feeding circuit L, upstream of such second actuator, by interposing second switching means between such second by-pass line B2 and such hydraulic feeding circuit L, the first and second switching means, each one of which is preferably made as at least one solenoid valve, respectively El, E2, being actuated by such control and management means C.

Within the system according to the present invention, the above actuators can be direct linear actuators (cylinders) or actuators through articulated mechanisms: for example, with particular reference to the Figures, the actuators can be a first and a second hydraulic motor, respectively Ml and M2, each one of which is preferably keyed-in directly on a respective worm screw of the system for lifting the platform of a truck for transporting motor vehicles or of a trailer, in such a way as to remove any mechanical interconnecting component: advantageously, both motors Ml and M2 are mutually equal, of an orbital type and, in order to guarantee a certain degreee of synchronism, are arranged in series along an hydraulic feeding circuit L by which they are actuated: with reference to the Figures, it is possible to note that, under the normal operation of the system 1 according to the present invention, the hydraulic feeding fluid through the hydraulic feeding circuit L firstly crosses the first motor Ml and therefrom it is sent to the second motor M2 before returning to the fluid tank (not shown) . In this way, since the two orbital motors Ml and M2 are identical, volumetric with the same displacement, the fluid flow-rate that crosses them is substantially the same and they will rotate approximately at the same rotation speed: the differences between the rotation speeds will be mainly caused by hydraulic leakages, by the imperfect symmetry of system and components, and by the not perfectly balanced load to be lifted. In order to compensate these errors, in the first preferred embodiment of the system 1 according to the present invention in FIG. 1, 2 and 3, the first detection means Rl are adapted to detect the angular displacement of the first motor Ml and the second detection means R2 are adapted to detect the angular displacement of the second motor M2.

As shown in the preferred embodiment of the system 1 in FIG. 1, 2 and 3, the first detection means Rl can be composed of at least one first phonic wheel Fl, operatively connected to the first motor Ml and rotated by this latter one during its operation, and of a respective first proximity sensor Sl communicating with such control and management means C. In parallel, the second detection means R2 can be composed of at least one second phonic wheel F2, operatively connected to the second motor M2 and rotated by this latter one during its operation, and of a respective second proximity sensor S2 communicating with such control and management means C.

In addition, it is possible to provide that the system 1 according to the present invention comprises means for detecting the movement direction of the actuators, and in particular of the rotation direction of the motors Ml and M2, cooperating with the control and management means C. In this way, since the counting is relative and not absolute, accuracy is improved and the progressive accumulation of errors is decreased: in fact, these errors are mainly due to the fact that, if the movement is stopped and reversed when only a half tooth offset was accumulated, the control and management means C could not correct or erroneosuly correct one tooth. This phenomenon can be repeated and can accumulate a progressive error upon every motion reversal. Moreover, this solution removes the defect of a possible response delay of the correction with respect to the command of the control and management means C. The detection of the rotation direction of the motors Ml and M2, but more in general of the movement direction of the actuators, can be performed by a suitable fifth sensor S5. In the preferred embodiment of the system 1 according to the present invention shown in FIG. 1, 2 and 3, the detection means Rl, R2, and in particular the two proximity sensors Sl and S2, then detect the movement of the motors Ml and M2 sending a digital signal to the control and management means C, which process such signals, by "counting" in particular the teeth of the two phonic wheels Fl, F2. When the control and management means C detect a difference between the two counts, and consequently a difference in angular displacement between the first motor Ml and the second motor M2, that therefore are not synchronised, they actuate the first or second switching means, and in particular the solenoid valve El or E2, related to the motor Ml or M2 that is faster, deviating the flow of the hydraulic feeding fluid from the hydraulic feeding circuit L to the respective by-pass line Bl or B2.

In particular, with reference to FIG. 2, it is possible to note that if the control and managing means C detect, through the comparison of signals detected by the detection means Rl, R2, that the first motor Ml rotates faster than the second motor M2, the control and managing means C actuate the first switching means, and in particular the first solenoid valve El deviating the flow of the hydraulic feeding fluid from the hydraulic feeding circuit L to the first by-passing line Bl: in this way, the hydraulic feeding fluid by-passes the first motor Ml that slows down till it stops, while the second motor M2 normally continues operating. When the control and managing means C detect, by comparing the signals detected by the detection means Rl, R2, that the rotation speed of the first motor Ml is again equal to that of the second motor M2, namely when the count of the teeth of the phonic wheels Fl, F2 by the proximity sensors Sl, S2 is "realigned", the control and managing means C again actuate the first switching means, and in particular the first solenoid valve El, deviating the flow of the hydraulic feeding fluid from the first by-passing line Bl to the hydraulic feeding circuit L, again feeding the first motor Ml and taking back the system 1 according to the present invention to its normal operating condition as shown in FIG. 1.

In parallel, with reference to FIG. 3, it is possible to note that if the control and managing means C detect, by comparing the signals detected by the detection means Rl, R2, that the second motor M2 rotates faster than the first motor Ml, the control and managing means C actuate the second switching means, and in particular the second solenoid valve E2, deviating the flow of the hydraulic feeding fluid from the hydraulic feeding circuit L to the second by-passing line B2 : in this way, the hydraulic feeding fluid by-passes the second motor M2 that slows down till it stops, while the first motor Ml normally continues operating. When the control and managing means C detect, by comparing the signals detected by the detection means Rl, R2, that the rotation speed of the second motor M2 is again equal to that of the first motor Ml, namely when the count of teeth of the phonic wheels Fl, F2 by the proximity sensors Sl, S2 is "realigned", the control and managing means C again actuate the second switching means, and in particular the second solenoid valve E2, deviating the flow of the hydraulic feeding fluid from the second by-passing line B2 to the hydraulic feeding circuit L, again feeding the second motor M2 and taking back the system 1 according to the present invention to its normal operating condition shown in FIG. 1. In any case, advantageously, the fact that the motors Ml, M2 are fed in series by the hydraulic feeding circuit L guarantees a certain degree of operating synchrony, even if the synchronising system 1 according to the present invention should fail.

With reference instead to FIG. 4, 5 and 6, it is possible to note that, alternatively, through the synchronising system 1 according to the present invention, it is possible to detect and correct the misalignment between two sides of the system for lifting the platform 3 of a truck for transporting motor vehicles (seen in the Figures in cross section) or of a trailer in a direct way, by comparing the inclination of the platform 3 to be lifted with respect to a chassis 2 of such truck. In this case, the first detection means Rl preferably comprise at least one third sensor S3 arranged so that it is integral with the chassis 2 or anyway with a part that is rigidly fastened thereto, and the second detection means R2 preferably comprise at least one fourth sensor S4 arranged so that it is integral with the platform 3 to be lifted, or anyway with a part that is rigidly fastened thereto. Preferably, both the third sensor S3 and the fourth sensor S4 are respectively an inclinometer or an accelerometer: the fourth sensor S4 then detects the angle formed of the platform 3 and the ground around an axis which is longitudinal to the vehicle, while the third sensor S3 detects the angle formed between the chassis 2 and the ground around the same axis. The signals of the two sensors S3, S4 are then sent to the control and management means C, that process them and compute the relative angle between platform 3 and chassis 2. The control and management means C then apply the correction to the actuators by acting on the means for switching the by-pass lines as previously described, in order to minimise the absolute value of the relative angle between platform 3 and chassis 2 .

In detail, always with reference to FIG. 4, 5 and 6, the two sensors S3 are S4 are sensitive to inclinations with respect to the ground along an axis which is parallel to the longitudinal vehicle axis (parallel to axis y of a rightwards triad xyz), by respectively measuring the angles α and β with respect to the ground. In FIG. 4, the ideal situation is shown of a platform 3 parallel to the chassis 2 (and this latter one parallel to the ground) in which the two measured angles are both null. Taking into account the positive counterclockwise and negative clockwise angles, it derives that: in FIG. 5 the platform 3 is inclined by an angle |β - α| with respect to the chassis 2 in which |β| < |α|, while in FIG. 6 the platform 3 is shown inclined by an angle | β — oc | in which |β| > I oc I . The hydraulic fluid is then sent to the actuators through mouths A and B, deviating the flow that from P (pump) goes towards T (tank) with the distributor D. The sensor S5, placed for example on the distributor, detects whether the imposed movement is along a direction or its opposite direction. The two sensors S3 and S4 measure the angles α and β related to the ground respectively of chassis 2 and of platform 3, the control and management means C process the signals from sensors S3, S4 and S5 and compute the correction angle |β - α| to be made, consequently- performing the correction in order to minimise the angle |β - α| by operating on the solenoid valve El or E2 according to needs .