GB2257102A

GB2257102A - A drive mechanism for a downhill belt installation.

Info

Publication number: GB2257102A
Application number: GB9212765A
Authority: GB
Inventors: Helmut Fleuchaus
Original assignee: Voith Turbo GmbH and Co KG
Current assignee: Voith Turbo GmbH and Co KG
Priority date: 1991-07-03
Filing date: 1992-06-16
Publication date: 1993-01-06
Anticipated expiration: 2012-06-16
Also published as: FR2678591B3; DE4122002C1; ITTO920535A1; GB9212765D0; IT1259591B; GB2257102B; ITTO920535A0; FR2678591A1

Description

1 2 2 5 -?1 t12 A drive-mechanism for a downhill belt installation The

present invention relates to a drive mechanism for a downhill belt installation of the type comprising an electric motor, a hydrodynamic coupling and a mechanical coupling. Such a drive mechanism is known from WO 82/04107 (EP 82 900 960); other drive mechanisms for downhill belt installations are based on simple configurations, such as, for example, a resilient connecting coupling between the electric motor and the driving shaft for the belt installation, or a hydrodynamic start-up coupling between the electric motor and the.-driving shaft.

In the known drive mechanisms the individual drive components always have such dimensions that they conform with the maximum energy requirement. With respect to the special case of a downhill belt installation, this means that' the individual components of the drive mechanism are designed to conform with the maximum energy requirement of the downhill belt.

However in downhill belt installations the conditions are completely specific. If the conveyor belt is still empty, i.e. unladen, lChen during start-up, i.e. when the belt installation is brought into service, only the amount of power required to overcome the frictional resistance in or at the various bearings has to be applied; this also applies with partly laden conveyor belts. As the loading of the belt installation increases, the flux of force (from the drive motor to the driving shaft) is reversed, as the loading of the conveyor belt no longer requires positive power from the 2 electric motor because of the dead weight acting on an inclined plane, but emits generated power thereto. Depending on the type of operation of the belt installation and on the loading condition, downhill belt installations therefore consume power (from the electric motor) or they release generated power (to the electric motor). As already mentioned, the individual components of the known drive mechanisms are always dimensioned so that they conform with the maximimn (generated) power requirement.

However in practical operation during the start-up of the empty conveyor belts only 10... 20% of the power requirement, which is preset and installed by computation, is needed; as the loading of the conveyor belt increases, the power requirement for the start-up operation is even less for the above-mentioned reasons. However as the dimensions of the driving motor conform with the load operation or operation at nominal rating, its dimensions for the start-up operation are (by necessi4i--y) excessive. As a resut during the start- up of the belt installation a high acceleration torque is produced. Thus the belt, the principal component of the belt installation, is very strongly loaded and particularly intensive longitudinal tensile vibrations on the belt are produced.

The object of the present invention is to improve the startup behaviour of a drive mechanism of the generic type so that the acceleration torque is reduced, but the high energy requirement for operation at nominal rating is retained without modification.

Claims

This objection is achieved according to the invention by the features set out in the characterising part of Claim 1. Thus, in accordance with the invention, during the sit-art-up operation the flow of flux directly from the electric motor towards the belt installation, i.e. by 3 "bypassing" the coupling via the hydrodynamic hydraulic coupling; therefore during start-up there is no positive connection to or via the coupling, win-ich acts as a synchronising device. If-the direction of the flow of flux is altered as a result of a negative load moment of the belt installation in 'Load operation (nominal rating), i.e. when torque is introduced to the electric motor, the torque transmission occurs - by "bypassing" the hydrodynamic hydraulic coupling from the belt installation directly to the coupling and from here to the electric motor. The advantage Of such an arrangwent resides in the fact that it can be designed to conform with the various conditions and requirements of the start-up operation via the hydrodynamic hydraulic coupling on the one hand and load operation at nominal ratir.a with the cooperation of the mechanical coupling on the other hand. The hydrodynamic hydraulic coupling is designed to conform with the lower positive energy requirement during start-up; the mechanical coupling is designed to conform with the maximum load requirement during operation at nominal rating, in which case the frictional connection from the belt installation to the electric motor then occurs by bypassing the hydrodynamic hydraulic coupling. The invention is described in more detail below by means of the drawings. Fig. 1 shows a basic representation of a downhill belt installation; Fig. 2 shows-'a basic or functional diagram of the drive mechanism; Fig. 3 shows a diagrammatic representation of a drive unit consisting of a mechanical coupling and a hydrodynamic hydraulic coupling; a Fig. 4 Shows a partial longitudinal section of an exemplified embodiment of the coupling shown in Fig. 3; Fig. 5 shows a diagrammatic representation of the motor torque during the start-up operation; Fig. 6 shows a diagrammatic representation of the torque of the driving shaft of the belt installation in start- up operation and in operation at normal rating. In Fig. 1 is represented a basic arrangement for a downhill belt installation 1. This consists of an endless conveyor belt 4 rotating between a driving shaft 2 and a guide roller 3 located lower down than said shaft. This conveyor belt 4 is loaded with material 5 to be conveyed in the region 9f the driving shaft 2 and transports it according to angle of inclination a of the conveyor belt A- to the valley or delivery station located in the region of the guide roller 3. In Fig. 2 is represented a basic connection diagram of a drive mechanism 10, by means of which the driving shaft 2 of a downhill belt installation 1 is to be driven. The energy required to operate the belt installation 1 is provided by an electric motor 11, which is preferably in the forni of a squirrel-cage motor. According to the present invention, the electric motor 11 acts during. start-up, i.e. when the belt installation 1 is brought into - service (c. f. arrow x), on a hydrodynamic hydraulic coupling 12, which is dimensioned to conform with 4- -art-up the relatively low power requirement for the sil- operation. The hydrodynamic hydraulic coupling 12 in turn acts on the driving shaft 2 of the belt installation 1 and sets it in motion according to the characteristic curve of the electric motor 11 or the start-up parabola of the hydraulic coupling 12. In the unladen'condition of the conveyor belt 4 of the belt installation 1, the amount of energy required to bring said belt into operation is only just enough to overcome the frictional and bearing forces of the belt installation 1. If in practical use the belt installation 1 is loaded, the conveyor belt 4 increasingly experiences acceleration forces, via which the driving shaft 2 of the belt installation 1 is increasingly stressed, so that there is no more power input by the motor. The electric motor 11 is now operated by a generating action via the driving shaft 2 of the belt installation 1. In this case so as to avoid the belt installation 1 accelerating unchecked, between the belt installation 1 and the electric motor 11 is inserted a mechanical coupling 13, which acts as a synchronising mechanism in so far that it inevitably maintains the synchronism between the belt velocity and the mains frequency of the electric motor 11. When the belt installation 1 operates at nominal rating or when loaded (c. f. arrow Y), the electric motor 11 is therefore operated by a generating action, in which case synchronism is guaranteed via the mechanical coupling 13. In Fig. 3 is shown a diagrammatic representation of a drive mechanism consisting of a mechanical coupling and hydrodynamic hydraulic coupling. The hydrodynamic hydraulic coupling 12 shown here for coupling the electric motor 11 with the belt installation 1 during or in start-up operation consists of a primary bucket wheel 21 rigidly connected (c.f. connection 40) with a primary shaft 20 (motor shaft) and a shell 22 appertaining thereto. Coaxially to the primary shaft 20 there is provided a secondary shaft 30 (third motion shaft) having a secondary bucket wheel 31, 6 which is connected to the driving shaft 2 of the belt installation 1. The shell 22 of the primary bucket wheel 21 is supported via a pair of rolling bearings 19 on the secondary shaft 30. To the secondary shaft (third motion shaft) 30 is attached a coupling member 32, which comprises two inner coupling discs, i.e. a rigid coupling disc 33 and an axially moveable coupling disc 34. In the coupling member 32 there is also disposed an annular cylindrical pressure chamber 35 having an axially displaceable annular piston 36 used to actuate the mechanical coupling 13. Finally on the coupling member 32 there is also mounted a storage chamber 37, the clear diameter of which is substantially smaller than that of the pressure chamber 35. The storage chamber 37 is connected via at least one connection line 38, which can be controlled via a valve 41, and also via at least two stoppage refilling ducts 42 dispaced by 180' with the pressure chamber 35. The pressure chamber 35 or the storage chamber 37 respectively are filled with a fluid, depending on the operating state. For the sake of completeness, please note that the two coupling discs 33/34 of the coupling member 32 are connected to one another via compression springs 39. The mechanical components 32... 39 described above form an operating part of the mechanical coupling 13; this coupling half is connected to the secondary shaft 30. A second coupling half - consisting of the components 23 and 24 - is rigidly connected to the primary shaft (c.f. connection 40). The mode of'operation of the drive mechanism shown in Fig. 3 is as follois: in the star,"%.-up condition the coupling between the motor 11 or the primary shaft 20 and the belt installation 1 or the secondary shaft 30 is based just on the action of the hydrodynamic hydraulic coupling 12. With respect to the 7 mechanical coupling 13, in the non-operative and start-up condition compression springs 39 keep the coupling 13 open. The rotation of the secondary shaft.30 has the result that a pressure dependent on the speed builds up as soon as the fluid also rotates. This causes the fluid to overflow from the storage chamber 37 into the pressure chamber 35, and in fact subsequent to the opening of a valve 41 operated by centrifugal force, which is located in the connection line 38. In the pressure chamber 35 the fluid pressure rises, because here the fluid rotates at a greater distance from the axis of rotation. If, at the end of the start-up operation, the speed has risen sufficiently, and if consequently the force of pressure acting on the annular piston 36 exceeds the restoring force of the compression springs 39, the annular piston 36 closes the mechanical coupling 13. In the load operation or operation at nominal rating the belt installation 1 is therefore exclusively coupled via the mechanical coupling 13 with the electric motor. In Fig. 4 is represented a possible structural development of the drive mechanism shown in Fig. 3. All important structural components are given the same reference numbers as in Fig. 3. The primary shaft 20 and the secondary shaft 30 are disposed coaxially to one another. The primary shaft 20 is connected via the rigid connection 40 with the second coupling half of the mechanical coupling 13 consisting of components 23 and 24 and also with the hydrodynamic hydraulic coupling 12. The first coupling half of the mechanical coupling 13 consisting of the components 32... 39 described in connection with Fig. 3 lies quasi inside a clearance limited by the connection 40 and the second coupling half of the mechanical coupling 13. 8 The rigid coupling disc 33 is constructed in two parts for reasons relating to production technology. Both parts are connected as an operational unit to the secondary shaft 30. The part 33a opposite the connection 40 is constructed and integrated in the arrangement so that firstly the pressure chamber 35 and secondly the storage chamber 35 is limited. The mechanical coupling 13 is shown in the open condition, i.e. the annular piston 36 abuts with almost its entire face (the lefthand surface in the drawings) so that the fluid is almost completely displaced into the storage chamber 37; in this case the fluid is almost completely separated from the annular piston 36. This occurs during stoppage via at least one of several refill ducts 42. The connecting pipe 38 leading from the storage chamber 37 to the pressure chamber 35 is first of all closed by valve 41. This means that during the start-up operation hardly any fluid pressure can build up on the annular piston 36. only when the motor synchronous speed has been reached is the 20 valve 41 dependent on the centrifugal force opened and the fluid released into the pressure chamber 35. The fluid pressure which quickly builds up in the pressure chamber 35 causes the closing of the mechanical coupling 13. In Fig. 5 is represented a diagram of the characteristic curve of the motor T,, and also - superimposed - the start up parabola P of the hydrodynamic hydraulic coupling 12. The abscissa of the diagram indicates the motor speed n,; the ordinate shows the motor torque T. When the electric motor 11 is connected, i.e. when the belt installation 1 is brought into service, the characteristic curve of the motor % shown for squirrel-cage motors of the known type used here is produced, which illustrates the loading of the hydrodynamic hydraulic coupling 12. From the start-up parabola P shown in the same diagram it can be seen 9 that the electric motor 11 intersects this start-up parabola P before its speed n.y. corresponding to the mains frequency is reached. In Fig. 6 is represented a diagram of the torques T, acting on the primary shaft 2 of the belt installation 1 and transmitted from the hydrodynamic hydraulic coupling 12. The abscissa shows the belt velocity n,; the ordinate indicates the torques T acting on the driving shaf t of the belt installation. In the start-up operation, i - e - with the f lux of f orce directed from the electric motor 11 via the hydrodynamic hydraulic coupling 12 to the belt installation 1, a torque T, acts on the empty belt, depending on the loading of the conveyor belt; a load moment T, acts on the fully loaded belt. The diagram also shows that for the start-up operation of the empty conveyor belt 4 a positive input f rom. the electric motor 11 is required, whereas with the f ully loaded conveyor belt 4 at the end of the start-up operation, i.e. when the motor speed and the belt velocity are synchronous to one another, a negative torque (load moment) and thus generated power is delivered. In the no- load condition of the conveyor belt, the belt velocity is always less than the motor speed. After the synchronous speed has been reached, the moment of the conveyor belt 4 corresponds with that of the electric motor 11, the motor torque T. acts against the intrinsic acceleration of the belt until operating point B is reached. By comparing the diagrams shown in Figure 5 and Figure 6, it can be seen in particular that, because of the relation between the characteristic curve of the motor TM and the start-up parabola P of the hydrodynamic hydraulic coupling 12, acceleration torques T, act on the empty conveyor belt 4.

1 CLAIMS R 1. A drive mechanism for a downhill belt installation, comprising an electric motor, a hydrodynamic hydraulic coupling and a mechanical coupling, wherein the hydrodynamic hydraulic coupling and the mechanical coupling are connected between said electric motor and the driving shaft for the belt installation such that, during start-up operation of the belt installation, torque tranmission from the electric motor to said driving shaft is performed exclusively via the hydrodynamic hydraulic coupling, and, during load operation, in response to a negative load moment on the belt installation caused by the load, torque transmission from the electric motor to the belt installation is performed exclusively via the mechanical coupling.

2. A drive mechanism according to claim 1, wherein the electric motor is a squirrel-cage motor.

3. A drive mechanism for a downhill belt installation constructed, arranged and adapted to operate substantially as hereinbefore described with reference to the accompanying drawings.