GB2172674A - Planetary gearing drive for a coal plane or chain type scraper conveyor - Google Patents

Abstract

A drive for a working machine such as a coal plane or chain-type scraper conveyor used in underground mining, comprises an electric motor (1) and a single-stage or multi-stage planet transmission (2). Sum wheels (10, 11) are fast on a drive shaft and engage with respective planet sets (8, 9) on a common carrier (7). Two rotatable annular gears (12, 13) are engaged with respective ones of the planets sets (8, 9) and are selectively brakeable. The carrier (7) preferably drives a second planetary stages (16) whose carrier is connected to the main output. The sum wheels (10, 11) may be driven via an elastic coupling or hydrodynamic coupling (3). The brakes may be located externally of the gearing housing, the annular gears (12, 13) being braked via intermediate gear wheels. The brakes are preferably automatically controlled by an electrohydraulic circuit primarily in dependence on the motor speed but also on the transmission oil temperature Fig. 2 (not shown). <IMAGE>

Description

SPECIFICATION Drive for a working machine The invention relates to a drive for a working machine comprising an electrical drive machine and a single-stage or multi-stage planet transmission.

The invention has particular but not exclusive application to machines in underground mining which are difficult to start, such as coal planes or chain-type scraper conveyors.

German patent application (DE-OS) No 33 23 251 shows a drive in which the planet transmission which is of a particular design configuration serves on the one hand as a step-down transmission with a fixed stepdown ratio and on the other hand as an overload clutch means which disconnects the electrical drive machine from the working machine in the event of overloading.

For working machines which are difficult to start, that is to say have to start on load with the drive machine starting and running up to speed with the working machine because shift clutches or shift transmissions cannot be used because of the particularities of the drive or the oder of magnitude of the power to be transmitted, electrical or hydraulic variablespeed drives can be used in most situations, in which drives the torque-speed ratio can be easily adapted to the condition of difficult starting. That adaptation effect essentially provides that the torque of such variable-speed drives, -at reduced speed of rotation and a uniform level of power, can be greater than the torque under normal operating conditions, often by a multiple, over prolonged periods.In those drives, suitable control and regulating means can provide a hyperbolic torque-speed relationship in which the torque automatically increases when the speed drops. Hydrodynamic couplings, which as regards the amount of space required and the purchase prices thereof are substantially less expensive than variable-speed drives, permit the working machine to be started up under low-load or loadfree conditions, over short periods of time, and in addition afford protection from overloading, also over short periods of time.

In many branches of the mining industry, in particular when mining pit or mineral coal, protection.from fire damp or an explosive atmosphere is an absolutely essential requirement because of the danger of the occurrence of explosive gases. Because of the individual outputs to be installed, which are frequently very high, and also because of the costs, compressed air can only be used sporadically as the drive energy. That means that three-phase asynchronous squirrel-cage motors are almost exclusively used as the drive machines, in which the characteristic, because of the steep limb between the pull-out torque and the noload speed, is in no way suitable for co-operating with working machines which are difficult to start. In many cases, for example in belt installations, that disadvantage is even now remedied by using hydromechanical clutches.

In the case of pit locomotives which are driven by those motors, hydraulic axial piston transmissions or hydromechanical converters are used.

The starting and operating performance of chain-type scraper conveyors, in particular the kinds which serve as longwall conveyors, and coal planes, for that reason gives rise to more problems than "normal" working machines which are difficult to start, because when dealing with material to be conveyed, which contains loam or heavy clay, and after prolonged stoppage times, for example at the weekends, high levels of torque for breaking loose are required when starting up the conveyors and, in the case of coal planes, the planes can suffer from blockage to such an extent as to come to a halt, in which respect in addition flyhweel moments of the drive are also applied to the chain.Such blockages, particularly when they occur in the vicinity of the drive, due to the working capacity of the chains being limited by stretching, result in overloading phenomena and in load peaks, chain breakages and a considerable reduction in the service life of the chains.

Initially, when the drive machines for chaintype scraper conveyors at the longwall and for coal plane installations were still 40 KW, later 60 KW and 80 KW, and the conveyors used double chain belts with chains with a wire thickness of 18 mm and the plane chain installations used chains with a wire thickness or gauge of 22 mm, it was usual for the disadvantages which arise in regard to the operation of coal planes and longwall conveyors from the characteristic of the three-phase asynchronous squirrel-cage motor to be reduced by using hydromechanical clutches. That resulted in particular in the chains being treated gently. In the course of further development, the operational concentration which is required for economic reasons resulted in a steady increase in the drive outputs and in going over to stronger and stronger chains.Overall drive outputs of 400 and 500 KW are no longer a rarity nowadays in relation to coal planes and longwall conveyors; chains of 30 and 34 mm wire thickness are in use, and a chain with a 38 mm wire thickness is being built. With the change to greater chain thickness, a considerable increase in service life and operational reliability of the chains would have been the expectation, but that was substantially compensated by the increase in drive outputs which occurred at the same time. Increasing the size of the chains resulted in a considerable increase in the weights involved and thus an increase in the proportion of output involved in moving the "dead loads", which in turn resulted in an increased amount of heat being generated and an increased amount of wear.At the depth at which mining goes on at the present time, such generation of heat which is in addition to the effects of ground or rock heat, which has a detrimental effect on the mine climate, causes serious problems; with increasing depth, in spite of the increased use of air conditioning and cooling machines, such generation of heat can no longer be accepted with safety. For that reason also it has therefore become an urgent necessity to develop drive systems with a start-up performance which treats the chains gently and which provides better protection from overloading than hitherto, in order to be able to use lighter chains with the same level of installed power.

In order to improve the start-up performance of coal planes and longwall conveyors, hydrostatic drive arrangements were also tested about 20 years ago, and in some places were used over prolonged periods of time. For a whole series of reasons, in particular because of the disadvantageous level of efficiency and the consequential development of an additional amount of heat under continuous operation conditions, it was not possible for those drives to be put into use successfully at that time.

Pole-switching motors in which the speed of rotation and thus the chain belt speed could be reduced in most cases in a ratio of 3:1 experienced a stormy development to the present state in which they are used almost exclusively. By virtue of their operating characteristics, it was possible, as it was desirable during the start-up procedure, to reduce the chain belt speeds in the start-up phase; it will be appreciated that higher torques were not available as the output was also correspondingly reduced, with the step down to the lower speed. When using pole-switching motors, it was no longer possible to use hydrodynamic coupling means so that the load on the chains during the start-up phase, in the event of fluctuations in load and stoppages, became considerably greater.Mechanically operating safety coupling means such as shear pin coupling means or star pin coupling means were used to an ever increasing extent to provide protection from overloading; although on the one hand such coupling means could limit the load peaks, on the other hand they gave rise to additional problems and cost.

The introduction of pole-switchable motors reduced and toned down but did not provide for in-depth elimination of the problems and difficulties which- arise by virtue of the fact that the characteristic of three-phase asynchronous squirrel-cage motors is not suitable for starting up coal plane installations and longwall scraper conveyors. The necessary elimination of the hydrodynamic coupling means which had the effect of subjecting the chains to careful treatment resulted in a considerable increase in load peaks in the load spectra of coal plane installations and scraper conveyors. For that reason, for some years now the German Pit Coal Mining Association (Steinkohlenbergbauverein) and the Westphalia Mining Union Office (Westfalische Berggewerkschaftskasse) have been carrying on research, the aim of which is to improve the drives for coal pleans and longwall conveyors.

According to the invention there is provided a drive for a working machine comprising an electrical drive machine and a single-stage or multi-stage planet transmission in which the electrical drive machine has a speed of rotation which varies little in continuous service, two planet wheel sets with different transmission ratios are disposed on a planet wheel carrier of the or one stage of the planet transmission, the two planet wheel sets are in engagement with two sun wheels arranged non-rotatably on the drive shaft of the respective stage and with two rotatable annular gear wheels and separately operable brakes are associated with the two rotatable annular gear wheels.

Such a drive can, without a high level of additional design expenditure, provide a suitably stepped load shift transmission and make it possible to use an electrical drive machine which has a speed that varies little in continuous operation, in particular a threephase asynchronous squirrel-cage motor.

The drive can provide a system which combines both a load shift transmission which is stepped in a suitable fashion, and also an overload protection means. This can be achieved without a high level of additional structure, thus giving a compact drive which is suitable for mining purposes. The power flow can be shifted or interrupted by simple, suitably controlled operation of the two brakes. When starting up and under overload conditions which build up slowly, account is taken of the fact that, with a reduced speed, over prolonged periods of time, greater reserves of power should be available in order to overcome the increased resistances in the working machine. In the case of overloads which occur suddenly, such as arise for example when the working machine is blocked or stalled, the working and drive machines are separated from each other without a substantial time delay, with the drive machine falling back to the idle state. After the blockage has been removed, the flow of power can be restored again without special steps, as are necessary for example when dealing with shear pin couplings, by simple shifting or switching operations. Hydrodynamic coupling means can again be used in order to subject the chain and the drive to gentle treatment.

The prime costs for the novel drive system can be considerably lower than with the drives which are used at the present time, involving pole-switchable motors, as normal three-phase asynchronous squirrel-cage motors are used and the additional safety coupling means can be eliminated because the overload protection means is a component of the shift transmission.

Particularly advantageous embodiments are recited in the subsidiary claims appended hereto.

The invention is diagrammatically illustrated by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view in crosssection through a drive for a working machine according to the invention; Figure 2 is a diagrammatic view of brake actuating means and associated hydraulic and electrical circuits for the drive of Fig. 1; Figure 3 is a fragmentary section as viewed showing rotatable hollow wheels of the drive of Fig. 1; Figure 4 is an elevation showing an arrangement of brakes and brake cylinders of the drive of Fig. 1; Figure 5 is a fragmentary sectional view showing a possible housing extension configuration with the gears for transmitting the movement, and the brake discs which are arranged outside the transmission, in the drive of Fig. 1;; Figure 6 is a schematic view of a working circuit for solenoids for actuating control spools or sliders in the drive of Fig. 1; and Figure 7 is a view of a planet carrier with two or more sets of planet wheels in a double housing mounting configuration comprising a variation of the drive of Fig. 1.

The basic structure of a novel drive system for working machines which are difficult to start can be seen from Fig. 1. Because of the high step-down ratio required in relation to coal planes and longwall conveyors, a threephase asynchronous squirrel-cage motor 1 is connected to a two-stage planet transmission 2. Instead of an elastic coupling 3, it is also possible to use a hydrodynamic coupling in order to subject drive chains to more gentle treatment. A connection 4 which is preferably in the form of a toothed or spline coupling transmits the output of the transmission 2 to a plane chain wheel 5 or a chain drum or star wheel of a chain-type scraper conveyor. In a first planet stage 6, a respective planet wheel carrier 7 carries two sets of planet wheels 8 and 9 which are of different diameters and which are arranged in pairs on the same axes of the planet wheel carrier 7.Sun wheels 10 and 11 are of co-operating diameters. Hollow gear wheels 12 and 13 which co-operate with the planet wheel sets 8 and 9 of the planet wheel carrier 7 are mounted fully rotatably in the housing of the planet transmission 2 and are of an annular configuration. Various alternative structures are possible for applying brakes (not shown in Fig. 1) to outside surfaces of the annular hollow gear wheels 12 and 13 and for directly taking off shift or switching pulses. Thus it is possible for example for the housing of the planet transmission 2 to be provided with recesses or openings (not shown), and for the brakes and the switching or shift devices to be disposed in those openings.It is further possible to provide apertures 14 and 15 in the housing of the planet transmission, through which the brakes and their actuating members and supply lines to the shift devices can be passed.

In that connection, it is possible to use both radially acting brakes and also disc-type brakes. In the construction shown in Fig. 5, the outside surfaces of the annular hollow gear wheels 12 and 13 carry toothed rings which act on gears 49 and 50 which extend through the apertures 14 and 15 and which in turn are connected to brake discs 56 and 57 and brakes and shift devices.

Reverting to Fig. 1, a second planet stage 16 of the planet transmission 2 is of a normal construction and a hollow gear 17 associated with the second stage 16 is a fixed component of the housing.

By alternately locking the annular hollow gears 12 and 13 by means of the brakes (not shown in Fig. 1), the planet transmission 2 becomes a load shift transmission, with the planet wheel carrier 7 rotating at different speeds in the two shift positions. In order to keep the forces, moments and mechanical loads at a low level, in the illustrated embodiment the first planet stage has been provided in the form of a shift stage. The shift operation itself, that is to say, the step of lifting off one brake and applying the other brake, can be damped by suitable control and actuating means, and can be carried out while avoiding peak loadings in respect of force and torque.

Simultaneous release of both brakes results in the flow of power and torque being interrupted so that that operation-triggered off by suitable sensors and actuating members -can fully perform the function of the safety couplings which are otherwise required to compensate for blocking, stalling or sudden overloading of the working machine. Interrupting the flow of torque or power in the abovedescribed manner further has the advantage that no additional components are required and normal operation, after elimination of the blocked or stalled condition, can be restored again by a simple shift operation. The safety function of the two annular hollow wheels or gears of the first stage 6 of the planet transmission may even be such that the brakes first slip under overload and lift off only shortly before inadmissible heating occurs.In that way the operating performance is approximated to the optimum coupling performance in regard to longwall conveyors and coal planes, in that, in the event of sudden overloads, the torque is initially maintained for a short period of time and then the flow of power is interrupted. If the resistance leading to overload or a blocking condition can be overcome after a relatively short period of time, then no interruption in the flow of power occurs with the above-described optimum coupling performance.

Hydraulic control for two brakes 18 and 19 may also be modified in relation to the configuration shown in Fig. 2, in that release of the brakes from the hollow wheels or gears can be effected not by hydraulic pressure but by spring force. By virtue of the dimensioning of the sun wheels 10 and 11, the planet wheels 8 and 9 and the annular hollow wheels 12 and 13 of both transmission stages, it is possible when shifting the transmission at least to achieve those speed relationships which are usually found nowadays when employing poleswitching motors. In addition it is also possible to achieve higher speed relationship which are not integers.

Fig. 2 shows the rotatable annular hollow gear wheels 12 and 13 of the first planet stage 6 as well as the associated brakes 18 and 19 with their corresponding brake cylinders 20 and 21. When the hollow wheel 13 is held by the brake 19, a low drive speed results which is required when starting up and when dealing with high loadings, while when the hollow wheel 12 is held by the brake 18, as shown in Fig 2, the arrangement provides normal operating speed in the drive. As different torques or speeds are produced by virtue of the two different step-down ratios of the transmission, with the same drive output in respect of the three-phase asynchronous squirrel-cage motor 1, higher forces are available for the low speeds of the coal plane or longwall conveyor, thereby very favourably affecting the operation of starting up the installation and over-coming high resistances.For the purposes of moving the brake cylinders 20 and 21, the arrangement has two servoactuated control slides or spools 22 and 23 which are preferably in the form of four-twoway valves, as well as a pressure generating system with a pump 24, a pressure storage means 25, a check valve 26, a safety valve 27 and a switching means (not shown) which can switch the pump 24 to pressure-less rotation when no pressure fluid is required. The pressure storage means 25 is intended to ensure the availability of an amount of fluid which is adequate for emergency operations, even in the event of problems at the pump.

The control spools 22 and 23 may be hydraulic-spring-loaded, electromagnetic or electromagnetic-spring-loaded in their mode of operation. A particularly advantageous alternative construction lies in the electromagnetic mode of actuation on both sides, as shown in Fig.

2, in which the various control pulses and measuring signals which are described in detail hereinafter and which must be taken into account in the various operating conditions, may be processed in the simplest manner.

In the control circuit, solenoids 28, 29, 30 and 31 are connected to associated switches 32, 33, 34 and 35 and a current source. The four switches 32, 33, 34 and 35 are actuated in different ways by various control pulses and measuring signals, in order to ensure a satisfactory drive performance in the start-up mode, in the normal operating mode and in an overload mode. In order to achieve the limit position shown in Fig. 2, in which the hollow gear wheel 12 is held, while the hollow gear wheel 13 can rotate freely, it is necessary to close the switches 33 and 34 while the switches 32 and 35 are left open.It is desirable for current to be caused to flow through the solenoids 28, 29, 30 and 31 only when switching over the control spools 22 and 23 so that the switches 32, 33, 34 and 35 are closed by suitable control and measuring signals for a given period of time, but are opened again after the change-over process has been completed. That may be achieved for example by a spring resetting effect (not shown) in respect of the switches 32 to 34, and an additional holding circuit with an interrupter contact (see Fig. 6).

The control pulses and measuring signals for actuating the four switches referred to above are transmitted by way of lines 36, 37, 38 and 39 of the control circuit. The most important switching operations which are necessary and which are to be triggered off in order to guarantee a satisfactory working performance in various operating conditions of the working machine, preferably when starting up and under overload, are described in detail hereinafter: Start-up procedure When the three-phase asynchronous squirrel-cage motor 1 is switched off, control pulses are automatically passed by way of the lines 36 and 39 to the switches 32 and 35 by means of which the control spools 22 and 23 are changed over, the brake 18 is released and the brake 19 is locked. That ensures that, when the three-phase asynchronous squirrelcage motor 1 is switched on, in any case the higher step-up ratio is initially operative in order to support start-up of the machine with the higher torques and lower speeds that are the result of that ratio. The speed of rotation of the three-phase asynchronous squirrel-cage motor 1 rises in accordance with the resistances to start-up of the chain-type scraper conveyor or coal plane. The increase in motor speed may be read off, obviously with the appropriate step-down factor, at the rotating hollow gear wheel 12, by way of a sensor 40 in the form of a digital pulse generator 40, and compared in a small memory (not shown), at intervals which are pre-programmed in respect of time, to the corresponding speed values of the motor characteristic curve.If, because of excessively high resistances to start-up, the pull-out torque in the start-up phase is not exceeded in a predetermined period of time, then the drive motor can also be stopped from there. When that torque is exceeded, then the change-over operation can be initiated in the small memory, at a predetermined limit speed of rotation, or it is also possible to delay the change-over operation until the maximum speed of the high step-up ratio stage, corresponding to the respective resistances to start-up, has been reached. The pulse for the change-over operation is then passed by way of a control line 42 to the control lines 37 and 38 which cause the change-over movement of the control spools 22 and 23 and which results in the hollow gear wheel 12 being locked and the brake 19 on the hollow gear wheel 13 being released.

In order to produce a "soft" switching operation, it is possible for delay members to be incorporated into the control lines and for throttle means to be provided in the hydraulic lines, which provide that release and locking of the brakes 18 and 19 take place slowly and in a particular predetermined times relationship.

If, instead of the elastic coupling 3 between the three-phase asynchronous squirrel-cage motor 1 and the planet transmission 2, a hydrodynamic coupling is used, then the speeds of rotation which are measured at sensor 40 and a similar sensor 41 on the rotatable hoi- low gear wheel 13 are no longer representative in respect of the speed of rotation of the drive machine in the respective transmission ratios which are operative in the transmission, because the slippage of the hydrodynamic coupling, which is dependent on load and which cannot be detected by way of the speed of rotation of the rotatable hollow wheels and which cannot be readily taken into consideration in the memories with a degree of accuracy which remains constant under operating conditions, is also included in the speed characteristics of the hollow wheels 12 and 13.In such a case therefore it is necessary for the measurement values for the speed of rotation of the three-phase asynchronous squirrel-cage motor 1 to be taken off directly at the output shaft thereof, for example by means of sensors which are disposed in the coupling housing or cage, and fed to the memories for triggering the control pulses.

Slow build-up of an overload In the brake position shown in Fig. 2 for the low transmission ratio of the transmission, that is to say, for "normal operation", a measurement in respect of the speed of rotation of the drive motor may be read off from the speed of rotation of the sensor 41, preferably a digital measurement value generator at the freely rotating hollow gear wheel 13. That measurement can be compared to the corresponding speed values of the motor characteristic curve in a small memory which is also not shown, and thus, just before the pull-out torque of the drive machine is reached, a pulse is applied by way of a control line 43 to the control lines 36 and 39, which triggers off the change-over operation for the high transmission ratio, that is to say, the lower speeds with the greater torques.That changeover operation may also be damped by means of delay members in the control lines and throttle means in the hydraulic lines, and thus can occur in a "soft" fashion.

Sudden occurrence of overloads for example upon blocking or stalling The sudden occurrence of heavy overloads or blocking or stalling may happen both in the slow gear (high step-up ratio) and also in the fast gear (low step-up ratio). Sudden overloads or blocking or stalling can be recognized by reference to a short-term severe drop in speed. That means that the speed values at the respective freely rotating hollow gear wheel drop very severely in an extremely short period of time. That steep drop in speed is recorded at the respective freely rotating measurement value generator, according to the gear which is then engaged, and is detected as a steep drop in speed in one of the two memories (not shown).The resulting pulse is passed by way of the control lines 42 and 43 to the control lines 36 and 38 and thus to the switches 32 and 34, with the result that both brakes are lifted off and both hollow wheels can rotate. In that way the drive machine and the working machine are immediately separated from each other and the flow of torque and power which passes through the drive arrangement is interrupted.

The electric motor falls back to the no-load speed. When the electric motor is switched off, the above-described control pulse which locks the brake 19 and releases the brake 18 occurs in order to allow the working machine to start up in the slow gear when it is switched on again after the blocking or stalling condition has been eliminated.

Additional temperature monitors for the brakes, the transmission oil and a hydrodynamic coupling The system of control lines 36, 37, 38 and 39, switches 32, 33, 34, 35, solenoids 28, 29, 30 and 31, control spools 22 and 23 and the brakes 18 and 19 for locking the hollow wheels 12 and 13 also makes it possible to use other than speed-dependent pulses for switching or shift operations or for interrupting the flow of power. Signals from suitable sensors which detect temperature may in that way produce switching operations which also considerably improve the operating perform ance of the drive.

Upon the occurrence of overloads which do not result in such a severe drop in speed as a blocking or stalling condition, it is, as already mentioned, for example a matter of great advantage if the torque can be maintained over a certain period of time before the flow of power is interrupted. That affords the possibility of maintaining an increased torque at greatly reduced speed within a given period, and thus possibly eliminating the resistance causing the overload condition. Transmission of the temporarily increaed torque, at reduced speed, may occur by providing that, in both speed stages of the arrangement, the brake which locks the respective hollow gear wheel which is to be locked is so set in regard to its braking force that it slips above a given level of torque. Precise setting of the braking pressure may be effected by means of pressure relief valves 44 and 45.If now the torque exceeds the limit torque which is fixed in that way, and if the hollow gear wheel slips under the brake shoes or pads, then the entire power of the drive machine is converted into heat between the brake shoes or pads and the discs driven by the hollow wheel, in a similar fashion as for example when using a start pin coupling. That transitional condition can only be maintained for a very short time and must be terminated by means of temperature monitors which are disposed in the brakes 18 and 19. The temperature monitors apply their pulses to the control lines 36 and 38 so that, after the limit temperature is reached, the or each locked brake is released and the flow of power is interrupted.

The temperature of the transmission oil may also be monitored by a temperature monitor which, when a critical limit temperture is reached, triggers off the same pulse and causes the flow of power to be interrupted.

Although the novel drive system for working machines which are difficult to start already has a whole series of decisive advantages in comparison with the conventional drives (poleswitching motor, transmission, safety coupling), the working performance may be further improved by the installation of a hydrodynamic coupling between the motor 1 and the transmission arrangement 2. The installation of a hydrodynamic coupling in that way is not possible when using pole-switching motors because there are no hydrodynamic couplings for different nominal speeds. A hydrodynamic coupling would contribute to an additional degree to reducing the loading on the chain in plane installations and longwall conveyors and in that way would increase the service life and considerably reduce the number of chain breakages and operating stoppages.In particular load fluctuations which do not result in the arrangement switching from one ratio to the other can be damped and their harmful effects on the working machine and the drive can be reduced. However hydrodynamic couplings suffer from the disadvantage that, under severe slippage which persists for a prolonged period, as usually occurs under overload conditions, the fluid experiences a substantial rise in temperature and safety fusible devices finally respond so that the oils runs out. That gives rise to considerable operating stoppages because the coupling must cool down and fresh oil be introduced.When using the novel drive system for working mahines which are difficult to start in conjunction with hydrodynamic couplings however it is possible to install sensors in the coupling cage or housing, which sensors permit contact-free transmission of measurement values which are representative of the fluid temperature, and in that way are capable of interrupting the flow of power in the transmission, by releasing both brakes, before the safety fusible device responds.

As shown in Fig. 3, on both sides of the two rotatable annular hollow gear wheels 12, 13, the arrangement has Simmering-like seals 43 co-operating with the transmission housing so that the apertures 14 and 15 can be provided outside the sealing means for sealing the housing against suffering oil losses therebeneath. It will be desirable for the region of the rotatable annular hollow wheels to be of such a configuration that annular chambers which are sealed with respect to the space inside the transmission are provided in the vicinity of the wall of the housing, said chambers communicating with the atmosphere. It will also be desirable for brakes and sensors to be protected from the ambient longwall area by dust seals.

Fig. 4 shows a possible arrangement of brakes and brake cylinders for an embodiment in which the brakes act radially on corresponding brake drums which are connected to the hollow gear wheels 12 and 13. In that arrangement the brakes and the brake cylinders are desirably interconnected by way of a rotatably mounted lever linkage.

Fig. 5 shows an embodiment in which, in order to make the sealing means for the transmision in a simpler configuration, the rotary movement of the hollow wheels 12 and 13 is taken off by way of the gears 49 and 50 which are arranged in a housing 51 fitted onto the housing of the transmission 2. In this embodiment, the working chamber of the transmission 2 and the chamber enclosed by the housing 51 are interconnected in such a way that the wheels can be lubricated jointly.

At the locations indicated at 52 and 53, shafts pass through the housing 51, with the gears 49 and 50 being mounted on the shafts on one side thereof, within the housing. The two shafts are sealed in a simple manner in the housing by seals 54 and 55. Carried on the free ends of the two shafts, which extend out of the housing portion 51, are the brake discs 56 and 57 on which the brakes act and which carry the sensors 40, 41 for producing the speed-dpendent signals. In that arrangement the brakes may once again be of a radially operative type or may be in the form of disc-type brakes.

Fig. 6 shows an embodiment of an electrical circuit diagram of working circuits which actuate the solenoids 28 to 31 when the switches 32 to 35 are closed. The corresponding fixed or rigid pulses for closing the switches are transmitted by way of the associated control lines 36, 37, 38 and 39, as already described.

A voltage source 58 which may not exceed a given voltage when the arrangement is used in operating pit coal mining, with protection from firedamp, supplies two circuits. In the first circuit, actuation of the switch 35 produces in a solenoid 59 an electromagnetic field which attracts an armature and closes a switch 60.

That provides that the current continues to flow even after the switch 35 is opened, and at the same time the circuit for actuation of the solenoid 31 is closed. That solenoid changes over the control spool 23, which may last for one or more seconds, when disadvantageous circumstances occur. For that reason the terminated change-over movement of the control spool 23 is confirmed by a switch 61 in that both the circuit for the solenoid 31 and also the circuit for the solenoid 59 are interrupted. The solenoids 59 and 61 must be spring-loaded at one side. That electrical switching action provides that the four working circuits for actuation of the four solenoids 28 to 31 have current flowing therethrough only during the change-over operations of the control spools 22 and 23.

In principle, the planet transmission 2 may also be provided with more than two speed stages (ratios) which are desirably in this case also put into the first planet stage as at that position the torques are still comparatively low and thus the forces which are to be applied by the brake cylinders are slight. If the shift stage of the planet transmission is provided with more than two planet wheels sets, it is desirable for the planet wheel carrier to be mounted doubly in the housing. Such an embodiment, although only for two planet wheel sets, is shown in Fig. 7. The shafts of the planet wheel carrier, on which the planet wheel sets 8 and 9 are disposed, are connected together by a ring 62 through which passes a shaft for the sun wheels 10 and 11.

The ring 62 is connected to the housing by way of an additional rolling bearing 63 so that the planet wheel carrier of the shift stage is mounted in the housing both at its output shaft and also at the ring 62. When the arrangement has more than two planet wheel stages, in that way the loadings on the planet wheel carrier and the deformation phenomena resulting therefrom can be reduced.

Claims (33)

1. A drive for a working machine comprising an electrical drive machine and a singlestage or multi-stage planet transmission in which the electrical drive machine has a speed of rotation which varies little in continuous service, two planet wheel sets with different transmission ratios are disposed on a planet wheel carrier of the or one stage of the planet transmission, the two planet wheel sets are in engagement with two sun wheels arranged non-rotatably on the drive shaft of the respective stage and with two rotatable annular gear wheels and separately operable brakes are asociated with the two rotatable annular gear wheels.

2. A drive according to claim 1, in which the brakes engage the outside periphery of the annular gear wheels or shafts, brake drums or brake discs which are directly connected or otherwise drivingly connected to the hollow wheels.

3. A drive accordingly to claim 1 or claim 2, in which the brakes are actuable by means of hydraulic brake cylinders.

4. A drive according to any one of claims 1 to 3, in which actuation of the two brakes is interlocked in such a way that only one of the two brakes can at any one time be brought into the holding position or both brakes can be brought into the freed position.

5. A drive according to claim 3, or claim 4 when appendant to claim 3, in which associated with the brake cylinders are pilot-controlled or servo-actuated control spools.

6. A drive according to claim 5, in which the control spools are actuable by solenoids.

7. A drive according to claim 5, in which the control spools are actuable by a hydraulic or pneumatic control circuit.

8. A drive according to claim 6 or claim 7, in which the control spools can be actuated in one direction by an electrical, pneumatic or hydraulic circuit and in the opposite direction by a spring loading.

9. A drive according to any one of claims 3 to 8, in which two pressure relief valves are disposed in the hydraulic circuit for actuation of the brake cylinders, the pressure relief valves limiting the pressure force in the brake cylinders in the holding position to predetermined adjustable values.

10. A drive according to any one of claims 3 to 9, in which disposed in the pressure line of the hydraulic circuit for actuation of the brake cylinders, downstream of a pressure generating pump, are a check valve and a safety valve.

11. A drive according to any of claims 3 to 10, in which a pressure storage means is disposed in the hydraulic circuit for actuation of the brake cylinders between the check valve and the control spools.

12. A drive according to any of claims 6 to 11, in which circuits and switches are pro vided for actuating the solenoids and by suitable control pulses can actuate the solenoids and thereby the control spools.

13. A drive according to claim 12, in which the switches are actuable by way of control lines and are in the form of quickbreak switches which open again after actuation thereof.

14. A drive according to claim 12 or claim 13, in which the circuits for actuation of the solenoids each comprise a control circuit and a holding circuit, and in which a solenoid in the control circuit actuates a switch which closes the holding circuit and maintains the flow of current in the control circuit.

15. A drive according to claim 14, in which after change-over of the control spools, a switch can be actuated, which interrupts the control circuit and thereby cuts off the current for the solenoid and interrupts the holding circuit indirectly by way of the switch.

16. A drive according to any one of claims 13 to 15, in which the control pulses for actuation of the switches can be triggered by sensors or by data storage means in which the measurement signals of the sensors are compared to predetermined programmed-in reference values.

17. A drive according to any one of claims 13 to 16, in which secured to the rotating annular gear wheels or the shafts, brake drums or brake discs which are directly or otherwise drivingly non-rotatably connected thereto are means, in particular iron cores or permanent magnets, which trigger a signal in associated sensors in each revolution.

18. A drive according to claim 17, in which said means are disposed in rings of non-metallic material which are fitted to the annular gear wheels or the brake discs.

19. A drive according to claim 17 or claim 18, in which the sensors which are responsive by way of said means are connected by way of control lines to a memory in which the signal pulses produced are compared with speed values of the drive machine, which are programmed in the memory, that is to say converted in analog manner by way of the respective step-down ratio.

20. A drive according to claim 19, in which the memory is connected to the control lines and delivers control pulses to the control lines at predetermined reference value-actual value relationships.

21. A drive according to claim 20, in which the control pulses which are triggered off in the memories relate to speed ranges of the drive machine, which are between the pullout speed and the no-load speed.

22. A drive according to any one of claims 13 to 21, in which disposed in the brakes are temperature sensors which, when a limit temperature is reached, apply control pulses to the control lines by means of which both brakes are simultaneously released.

23. A drive according to any of claims 13 to 22, in which a hydrodynamic coupling is installed between the drive machine and the planet transmission, the temperature of which coupling is monitored in a contact-free manner from a coupling cage or housing and, when a limit temperature is exceeded, the corresponding sensor triggers release of both brakes by way of the control lines.

24. A drive according to claim 23, in which the measuring means for measuring the speed of rotation of the drive machine is arranged at the shaft of the drive machine, in particular beneath a cage or casing of a hydrodynamic coupling.

25. A drive according to any one of claims 13 to 24, in which disposed in transmission oil of the planet transmission are temperature sensors which, when a limit temperature is exceeded, trigger a control pulse which triggers immediate release of the two brakes by way of the control lines.

26. A drive according to any one of claims 13 to 25, in which the brakes can be loaded in the opening direction by spring force and in the braking direction by the hydraulic cylinders.

27. A drive according to any one of claims 1 to 26, in which the hollow gear wheels are sealed by annular gap sealing means at both sides with respect to the housing of the planet transmission and disposed in the transmission housing in the region of the annular gear wheels are apertures through which extend the brakes and the lines for the sensors.

28. A drive according to claim 3, in which disposed on the annular gear wheels are gear rings from which the rotary movements are taken off by way of gears and transmitted to the brake discs.

29. A drive according to claim 28, in which the gears are arranged in a housing extension portion which is connected to the remainder of the housing of the planet transmission in such a way as to permit common lubrication of all moving parts and gears belonging to the planet transmission.

30. A drive according to claim 29, in which extending through the housing extension portion are shafts on which the gears are arranged within the housing extension portion, and thus in the region of the lubrication and on which the brake discs are arranged outside the housing extension portion.

31. A drive according to claim 30, in which sealing means in the form of shaft seals are provided at the locations at which the shaft pass through the housing extension portion.

32. A drive according to any one of claims 1 to 31, in which the shafts of the planet wheel carrier on which the planet wheel sets are arranged are connected at their free ends by way of ring which in turn is rotatably mounted by way of a rolling bearing in the housing of the planet transmission.

33. A drive for a working machine substantially as hereinbefore described and illustrated with reference to the accompanying drawings.