GB2074258A - Change-speed gearbox - Google Patents

Abstract

A speed-change gearbox 1 comprises a housing 2 containing a rotatable input shaft 3 connectable to a prime mover and carrying a pinion 5, a rotatable and co-axial output shaft 17 carrying a plurality of speed reduction gears 15, 16 and a plurality of lay shafts 7. Each lay shaft 7 carries a gearwheel 6 in mesh with the pinion 5 and a hydraulically operable clutch 11 through which a respective transmission gear 14 in mesh with an individual speed reduction gear 15, 16 is driven. A hydraulic pump is driven by one of the lay shafts 7 for supplying hydraulic fluid to each clutch 11. The output shaft 17 is connected to the input shaft 34 of an epicyclic reduction stage 35, a torque sensing device being connected between the annulus 41 and the housing. <IMAGE>

Description

SPECIFICATION Gearbox This invention relates to a speed-change gearbox suitable for driving a conveyor, e.g. of the scraper chain or belt type.

Scraper chain conveyors are used extensively in coal mining operations and are driven from an electric motor via a fluid coupling and a speed reduction gearbox. However, demands for increased horse-powers for the conveyors have led to difficulties with fluid couplings and in particular in providing adequate cooling of these couplings, and the present invention provides a speed-change gearbox intended, amongst other things, to enable a fluid coupling to be eliminated from a conveyor drive.

According to a first aspect of the present invention, a speed-change gearbox comprises a housing containing a rotatable input shaft connectable to a prime mover and carrying a pinion, a rotatable and co-axial output shaft carrying a plurality of speed reduction gears, a plurality of lay shafts each rotatable about individual axes spaced from, and parallel to, the axis of the input and output shafts, and each lay shaft carrying a gear wheel in mesh with the pinion, first elements of a hydraulically operable clutch being carried externally by each lay shaft and second elements of the clutch being carried internally by a coaxial sleeve, one of which surrounds a portion of each lay shaft, each sleeve carrying a transmission gear in mesh with an individual speed reduction gear, a torque sensing device operable to halt the prime mover upon a prescribed torque being exceeded, and a hydraulic pump drivable by one of the lay shafts for supplying hydraulic fluid to each clutch, the output shaft being connected to the input shaft of an epicyclic reduction stage contained within the gearbox housing and incorporating an annulus mounted in bearings, the torquf sensing device being connected between the annul us and the housing to restrain rotary movement of the annulus.

Thus, with the input shaft connected to a prime mover, e.g. an electric motor, rotation of the pinion rotates the lay shafts in mesh with that pinion and the hydraulic pump, but provided no clutch is engaged, no rotation is obtained at the output shaft, the admission of hydraulic fluid supplied from the pump to a selected clutch gradually commencing rotation of the output shaft via the sleeve and transmission gear of the selected clutch and the particular reduction gear in mesh with that transmission gear with the torque transmitted being continuously monitored by the torque sensing device.

The torque sensing device provides of course for overload protection in the case of a speed reduction, where a consequent increase in torque occurs.

Therefore, basically, if a two-speed gearbox were required, then a pair of speed reduction gears would be provided on the output shaft and two lay shafts would be provided, the transmission gear of one lay shaft being in mesh with one of the reduction gears, and the transmission gear of the other lay shaft being in mesh with the other reduction gear. It follows that the gearbox housing needs to be apertured at two locations to provide access to ends of the input shaft and an epicyclic output shaft. Such ends may be male or female and may be splined or keyed etc., for whatever particular form of connection is required at these ends.

If still further speed reduction is required, the output shaft of the epicyclic reduction stage may be connected to the input shaft of a further reduction stage. The requirements for particular speed reductions will of course depend on whether the gearbox is intended for transmitting power to a conveyor, where further speed reduction would be required.

In detail, the torque sensing device may be connected electrically to an electric motor constituting the prime mover, to switch off the motor upon a predetermined torque being exceeded.

Furthermore, there is also currently a demand for the provision of a braking action to obtain positive braking on a conveyor after its drive has been switched off, rather than, as has in the past occurred with scraper chain conveyors, allowing the conveyor to halt within a few feet, after its drive has been switched off, due to the inherent friction of, and or load on, a scraper chain conveyor. Although a braking lay shaft could be provided, a braking effect is obtained if both clutches of the lay shafts are simultaneously operated.

Finally, with scaper chain conveyors, it is frequently necessary to tension and de-tension the chain(s) of the conveyor, e.g. for chain or flight bar repair or replacement. Therefore, in accordance with a further aspect of the present invention, the gearbox is provided with a tensioning lay shaft, a co-axial sleeve surrounding a portion of this lay shaft, a clutch to interconnect the lay shaft and sleeve, and a transmission gear of the sleeve in mesh with a speed reduction gear, and an additional motor to drive the tensioning lay shaft.

The additional motor may be a hydraulic motor driving a worm in mesh with a worm wheel of tensioning lay shaft, so that tensioning can be effected with the prime mover deactivated.

Thus, in detail, a two-speed gear box with both braking and chain tensioning facilities would comprise three lay shafts, two located in a common diametral plane and the third located at 900 to that plane.

The invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an axial sectional view through a speed change gearbox in accordance with the invention; Figure 2 is a half end view on arrow A of Figure 1 and half section on the line Il-Il of Figure 3; Figure 3 is also an axial sectional view similar to Figure 1 but taken on the line Ill-Ill of Figure 4; Figure 4 is a half end view on arrow B of Figure 3 and half section on the line lV-IV of Figure 3; and Figure 5 is a section on the line V-V of Figure 4.

In the drawings, the gearbox, indicated at 1, comprises a housing 2 rotatably supporting a female, internally splined input shaft 3 rotatable about an axis 4. The input shaft 3 receives a male, externally splined drive shaft (not shown) of an electric motor to which the gearbox 1 is bolted.

The input shaft 3 carries a pinion 5 permanently in mesh with gearwheels 6 of two, speed reduction lay shafts 7 rotatable about axes 8 spaced from, and parallel to, the axis 4, and located in a common diametral plane 9. Each lay shaft 7 also carries first elements 10 of a hydraulically operable clutch 11 with second elements 12 carried internally by a sleeve 13 co-axially surrounding a portion of its lay shaft. Each sleeve 13 carries a transmission gear 14, permanently in mesh with one or two individual speed reduction gears 1 5, 1 6 carried by an output shaft 1 7 rotatable about an axis 18 co-axial with the axis 4.

A tensioning lay shaft 19, rotatable about an axis 20 parallel to axes 1 8 and 4, is provided at one end with a wormwheel 21 in mesh with a worm 22 drivable by a hydraulic motor 23 and is also provided with a co-axial sleeve 24 having a transmission gear 25 permanently in mesh with one speed reduction gear 1 5. A clutch 26 serves to interconnect the lay shaft 1 9 and the sleeve 24 when chain tensioning or de-tensioning operations are required, by a slide sleeve 27 pivoting clutch operating levers 28, the slide sleeve 27 being displaceable along a tubular member 29 by means of a pair of spaced apart, forked, bell cranks 30 (one only visible in Figure 3) operable by a hand lever (not shown) mounted at one end of a shaft 30A carrying the bell cranks 30, with a hydraulic piston and cylinder unit 31 serving to prevent operation of the hand lever and hence engagement of the clutch 26 when the electric motor is running.

The output shaft 1 7 terminates at one end at its end remote from the pinion 5 in a female, internally splined coupling element 32 which receives a male externally splined end 33 of an input shaft 34 of an epicyclic gearbox 35. At its other end the shaft 34 terminates in a sun wheel 36 in mesh with planet wheels 37 carried by a carrier 38 rotatable about an axis 39 parallel to the axes 1 7 and 4 and terminates in a bevel gear 40 adapted to mesh with a bevel gear (not shown) of a transmission to a conveyor. The planet wheels 37 are also in mesh with an internally toothed annulus 41 mounted in bearings and provided with outer and inner face plates 42, 43, respectively.To the face plates are welded inner and outer rotation rings 44, 45, respectively rotatable around circumferential faces 46 of the gearbox housing 2 and contained by shoulders 47.

The inner face plate 43 has an extension 48 with an aperture 49 to receive a pivot pin 50 for connecting a torque sensing device 51 between the annulus 41 and a rigid plate 52 welded to the housing 2, the torque sensing device being electrically connected to the electric motor Thus, rotation of the annul us 41 is constrained by the torque sensing device 51 (and by an insignificant amount of friction at faces 46 and shoulders 47) and hence the torque sensing device 51 can be pre-set to allow a predetermined torque level to be attained which level when exceeded, e.g. by an unusual load being imposed on the conveyor or by the conveyor becoming jammed, triggers the torque sensing device 51 to switch off the electric motor, thereby preventing unnecessary damage to the electric motor, the gearbox 1, and the subsequent transmission to the conveyor.

Hydraulic fluid for operation of the clutches 11 is provided by a pump 52 located internally of the housing 2 and having a gear wheel 53 permanently in mesh with one gear wheel 6.

Claims (9)

1. A speed-change gearbox comprising a housing containing a rotatable input shaft connectable to a prime mover and carrying a pinion, a rotatable and co-axial output shaft carrying a plurality of speed reduction gears, a plurality of lay shafts-each rotatable about individual axes spaced from, and parallel to, the axis of the input and output shaft, and each lay shaft carrying a gear wheel in mesh with the pinion, first elements of a hydraulically operable clutch being carried externally by each lay shaft and second elements of the clutch being carried internally by a co-axial sleeve, one of which surrounds a portion of each lay shaft, each sleeve carrying a transmission gear in mesh with an individual speed reduction gear, a torque sensing device operable to halt the prime mover upon a prescribed torque being exceeded, and a hydraulic pump drivable by one of the lay shafts for supplying hydraulic fluid to each clutch, the output shaft being connected to the input shaft of an epicyclic reduction stage contained within the gearbox housing and incorporating an annulus mounted in bearings, the torque sensing device being connected between the annulus and the housing to restrain rotary movement of the annulus.

2. A gearbox as claimed in Claim 1, wherein a pair of speed reduction gears are provided on the output shaft and two lay shafts are provided, the transmission gear of one lay shaft being in mesh with one of the reduction gears, and the transmission gear of the other lay shaft being in mesh with the other reduction gear.

3. A gearbox as claimed in Claim 1 or Claim 2, wherein the gearbox housing is apertured at two locations to provide access to ends of the input shaft and an epicyclic output shaft.

4. A gearbox as claimed in any preceding Claim, wherein an output shaft of the epicyclic reduction stage is connected to the input shaft of a further reduction stage.

5. A gearbox as claimed in any preceding Claim, wherein the torque sensing device is connected electrically to an electric motor constituting the prime mover, to switch off the motor upon a predetermined torque being exceeded.

6. A gearbox as claimed in any preceding Claim, wherein a braking lay shaft is provided.

7. A gearbox as claimed in any preceding Claim, provided with a tensioning lay shaft, a co-axial sleeve surrounding a portion of this lay shaft, a clutch to interconnect the lay shaft and sleeve, and a transmission gear of the sleeve in mesh with a speed reduction gear, and an additional motor to drive the tensioning lay shaft.

8. A gearbox as claimed in Claim 7, wherein the additional motor is a hydraulic motor driving a worm in mesh with a worm wheel of the tensioning lay shaft.

9. A speed-change gearbox substantially as hereinbefore described with reference to the accompanying drawings.