GB844955A - Improvements in or relating to locking devices or sprags for gear wheels - Google Patents

Abstract

844,955. Excavators. AVELING-BARFORD Ltd. July 18, 1958 [July 30, 1957], No. 24132/57. Class 68(1). [Also in Groups XXIV and XXX]. In a locking device, particularly for locking the rotatable superstructure of an excavator or crane, wherein a dog 16 is moved, e.g. manually, into and out of engagement with the internal or external teeth of a gear 10, the dog 16 moves in a plane 24 which is parallel to a radial plane 13 and is spaced from it by a distance such that the gear tooth flank exerts only a negligible component of force in the plane 24, i.e. the tendency to disengage under gear torque is negligible. As shown two pairs of dogs 15, 16 and 17, 18 are formed on a sprag 11, Fig. 2, mounted on a shaft whose axis 12 is perpendicular to a radial plane 13 of a gear 10 having flat-sided internal teeth. Bosses 14 prevent axial movement of the sprag. The tangents to the tooth flanks contacted by the dogs 16 and 17 lie in the planes in which the dogs move so that they experience no tendency for disengagement. The tangents (such as 27) to the tooth flanks contacted by the dogs 15 and 18 are inclined slightly to the planes in which the dogs move so that the dogs experience a slight tendency for disengagement. The spacing of the plane 24 from the plane 13 is the product of the pitch circle radius and the sine of the pressure angle P. It is stated that the spacing of the plane of movement of any dog should not differ from this product by more than twice the gear tooth pitch. In a modification, Fig. 3 (not shown), a locking sprag co-operates with a gear having external involute teeth. When applied to a crane or excavator having an undercarriage 45, Fig. 5, on wheels or tracks 46 and a superstructure 43 mounted to rotate on rollers 44, the locking device comprises an internally-toothed gear ring 47 on the undercarriage co-operating with a sprag 11 as shown in Fig. 1, the sprag being rotated about stub shafts 52 by a hand lever 58 linked, preferably adjustably, thereto. The lever 58 is preferably provided with a latch 59 cooperating with a slotted quadrant 60.