OVERLOAD-PROTECTED GEAR

Abstract: A gear transmission for overload protection of a drive-system comprising a main shaft (10) and a first gear (20) mounted on the main shaft (10), said first gear (20) being in mesh with a second gear (25), which is secured on a short counter shaft (11) extending in a direction parallel to the main shaft and flexibly and resiliently sus­ pended, and a third gear (21) in mesh with a fourth gear (26) with the same axis of rotation as the first gear (20). In order to obtain a system which is sturdy and durable, and suited for receiving and transmitting positive as well as negative torques and which simultaneously gives a reliable indica­ tion, if the torque exceeds a given threshold value, it is suggested that the main shaft is suspended in a bearing frame (5) suspended on the main shaft (10) and fixed between spring means (67, 68) re­ silient in peripheral direction in a plane perpen­ dicular to the main shaft.

Description: The present invention relates to a gear transmission for overload protection of a drive-system comprising a main shaft and a first gear mounted on the main shaft, said first gear being in mesh with a second gear which is mounted on a short counter shaft ex­ tending in a direction parallel to the main shaft and flexibly and resiliently suspended, and a third gear in mesh with a fourth gear with the same axis of rotation as the first gear is further mounted on said counter shaft, all gears being of the type comprising an external cogging, and in which a move­ ment of the counter shaft is sensed by sensor means. EP Patent 042 801 discloses a gear transmission of this type, in which the counter shaft is displace­ able in its longitudinal direction, and in which the first and the second gears are provided with helical or inclined teeth so that the counter shaft during transfer of power is influenced by a force attemp­ ting to displace the counter shaft in its longitu­ dinal direction towards a helical spring or a cup spring, which is compressed, and in which a switch capable of switching off an engine current is moun­ ted at the end of the shaft. The gear transmission is only overload protected in one direction of rotation. Several overload protected pinions with planetary transmission are known. Such pinions are inter alia described in DE Patent Specification 30 10 019 and US Patent Specification No. 3,613,853. Wherever a power is transmitted through a trans­ mission in a system, it is desirable to protect the system against overloads by disconnecting the engine, if the load torque exceeds a given threshold value. It is consequently the object of the present in­ vention to provide a device of the above type, which is simple and inexpensive in manufacture, sturdy and durable and is adapted to receive and transmit both positive and negative torques. This object is according to the invention obtained by the counter shaft being suspended in a U-shaped bearing frame or pedestal pivotally suspended round the main shaft on each side of the first gear and being fixed between spring means which are resilient in a substantially peripheral direction in a plane perpendicular to the main shaft, or in other words in such a manner that the counter shaft is capable of moving in a short circular arc situated in a plane perpendicular to the main shaft and with its centre on the axis of rotation of the main shaft. The suggested construction has the essential ad­ vantage that the complete meshing is maintained, there being no axial or radial interdisplacement of the gears. The free end of the bearing frame is preferably connected with a sensor device comprising a pointer registration for reading the size of the currently transmitted torque. The suggested system may be used wherever a driving engine is to pull mechanical installations, e.g. transport installations, up- and over doors, auto­ matically opening and closing windows etc., and engine, toothed bars, worm wheels, window fittings etc. are efficiently protected against overload. The newly developed system is furthermore advan­ tageous by being suitable for being built into a closed gear box easily mounted on the main shaft. The invention will be described below with reference to the accompanying drawing, in which Figure 1 is a simplified sectional view through the main shaft and the counter shaft of the most im­ portant parts of a system according to the inven­ tion, Figure 2 is a left-hand view of the parts of Figure 1, Figure 3 is a sectional view through the main shaft and counter shaft of a second embodiment of the gear transmission, Figure 4 is a gear transmission in a gear box. Figure 1 illustrates the most important elements of the new gear transmission. The main shaft 10 is through-going and is provided with gears 10 mounted on and rotating together with the main shaft 10. The gear 20 is in mesh with a counter wheel 25 ro­ tating round a displaceable shaft 11, the shaft 11 being suspended in a socalled bearing frame 5. This bearing frame is U-shaped and supported on the shaft in bearings on both sides of the first gear 20. The counter shaft 11 and the main shaft 10 extend through the bearing frame 5, and the bearing frame is tiltable or slightly rotatable round the main shaft, its movements are, however, restricted, as it is fixed in its free end e.g. as illustrated in Figure 2 by means of a bolt 14 between disk-­ shaped springs 67, 68. In its other end the counter shaft 11 has a third gear or counter wheel 21 cap­ able of rotating together with the counter shaft. Said third gear 21 is drivingly connected to a fourth gear 26 situated on a worm wheel 22 with the same axis of rotation as the first gear 20 but freely pivotal in relation to the main shaft 10. The worm wheel is driven by a worm (not shown), which is driven by an electromoter (not shown). In its preferred embodiment the gear transmission is developed for opening and closing skylights in a greenhouse and preferably placed midway in the the main shaft extending in the entire length of the greenhouse. The main shaft may be provided with toothed gears opposite each skylight, which can be opened and closed by the toothed gear via a toothed bar. The new gear transmission may of course also be placed at the end of the main shaft. When the row of windows is to be opened and closed, the engine is started and drives the worm, which drives the worm wheel 22 with the adjacent gear 26, and through the gear 21, the counter shaft 11, the gear 25, the gear 20 and the main shaft 10 the driving torque is transferred to the various rack- and- pinions placed opposite each window. In case of jamming, optionally caused by a jammed window, the main shaft 10 will hardly be able to rotate. A driving power on the worm wheel will then have the effect that the displaceable counter shaft attempts to move in a circular arc round the main shaft 10. This movement can be used for re­ gistering a hindrance somewhere. The free end of the bearing frame will be displaced out of its position of rest in the centre between the two sets of springs 67, 68. This displacement of the free end of the bearing frame may be used for dis­ playing the size of the driving torque on the main shaft. In the embodiment illustrated in Figures 1 and 2 the free end 38 of the bearing frame 5 engages a gear 28 by way of a toothed bar 29. The gear 28 or the shaft 13, on which the gear is situated, is again connected with a pointer or an arm 70. A micro-switch (not shown) switching off the electro­ motor is arranged in the right and the left outer­ most position, respectively, influenced either by the arm, the toothed bar or the bearing frame. It is obvious that the gear transmission described is not restricted for use in a greenhouse, and that the gear transmission may be used wherever motordriven installations, e.g. transport systems, machine tools, motordriven up- and over doors etc., comprising a gear drive should be protected against overload. In another embodiment illustrated in Figure 3 the main shaft is not through-going and the fourth gear 26 is mounted directly on an engine. The part of the bearing frame farthest away in relation to the main shaft is preferably arranged to actuate sensor means. The toothed bar 29 is as illustrated in Figure 2 mounted on the outermost end of the bearing frame to obtain maximum movement for actuating a sensor means, such as the gear 28 with the pointer arm 70. The switch or micro-switch capable of switching off the electromotor may ad­ vantageously be located outside the gear trans­ mission system, which is expediently embedded in a closed oil-filled gear box 2 in Figure 4, in which only the main shaft 10 and the shaft for monitoring the torque are illustrated. The switch may e.g. be mounted in a closed box 50 on one side of the gear box 2. The switches are mounted in such a manner that a specific rotation of the shaft for monitoring the torque in one direction will switch off the engine, and a given rotation, optionally bigger or smaller than the first one, is also capable of switching off the engine. Furthermore, a poten­ tiometer is preferably mounted directly on the shaft 13, or in mesh with the shaft 13, so that the size of the torque can be registered electrical­ ly. A feedback to a control or regulating unit for the installations may be obtained by means of a built-­ in potentiometer. The described construction may consequently be used both as an alarm function and as a supervising or measuring function. The inventive gear transmission may be used as a unit for sensing a torque and may be built into a system without regard to other transmissions, if any. The inventive transmission can together with a driving engine be used as a complete driving unit. The inventive gear transmission allows a continuous supervision of the load torque in a drive-system. The construction is particularly advantageous by the complete tooth meshing being maintained even under the maximum allowable loads. As a result an efficient power transfer and besides less wear on the gears are obtained. A particular advantage is that the built-in spring effect simultaneously protects all the components forming part of the drive-system, all suddenly arising shock stresses being averted at least par­ tially.

Claims: 1. A gear transmission for overload protection of a drive-system comprising a main shaft (10) and a first gear (20) mounted on the main shaft (10), said first gear (20) being in mesh with a second gear (25) which is secured on a short counter shaft (11) extending in a direction parallel to the main shaft and flexibly and resiliently suspended, and a third gear (21) in mesh with a fourth gear (26) with the same axis of rotation as the first gear (20) is further secured to said counter shaft (11), all gears being of the type comprising an external cogging, and in which a movement of the counter shaft (11) is sensed by sensor means, cha­ racterised by the counter shaft being sus­ pended in a U-shaped bearing frame or pedestal (5) pivotally suspended round the main shaft (10) on each side of the first gear and being fixed between spring means which are resilient in a substantially peripheral direction in a plane perpendicular to the main shaft. 2. A gear transmission as claimed in claim 1, characterised in that the bearing frame is connected with the sensor means. 3. A gear transmission as claimed in claim 2, characterised in that the part of the bearing frame (5) farthest away in relation to the main shaft is arranged to actuate the sensor means. 4. A gear transmission as claimed in claim 1, and in which the fourth gear is driven either di­ rectly or indirectly by an engine, charac­ terised in that the bearing frame is arranged to actuate switching means adapted to switch off the engine. 5. A gear transmission as claimed in one or several of the preceding claims, charac­ terised in that the bearing frame (5) is connected to registering means for reading the size of the currently transmitted torque. 6. A gear transmission as claimed in claim 5, characterised in that the registering means comprise a potentiometer mounted on a shaft (13) influenced by the movement of the bearing frame (5). 7. A gear transmission as claimed in one or several of the preceding claims, charac­ terised in that the main shaft is through-­ going, and that the fourth gear is pivotally sus­ pended round the main shaft and is situated together with a driving wheel driven by a driving engine. 8. A gear transmission as claimed in claim 7, characterised in that the fourth gear is situated together with a worm wheel driven by the driving engine through a worm pinion. 9. A gear transmission as claimed in one or several of claims 1-5, characterised in that the main shaft is not through-going and terminates at the fourth gear, said fourth gear being the driving wheel and preferably mounted directly on an engine located with the same axis of rotation as the main shaft.

Inventors: HANSEN, POUL HENNING
Applicants: DANSK GARTNERI-TEKNIK A/S
Application year: 1986
Main classification: F16H35
IPC codes: F16H35