GB1451330A - Hitch assembly - Google Patents

Abstract

1451330 Scraper bowls CATERPILLAR TRACTOR CO 4 Sept 1973 [5 Sept 1972] 19598/76 Divided out of 1451329 Heading E1F [Also in Divisions B7 and F2] A bowl scraper 15, Fig. 1 is supported on a tractor 13 by a hitch assembly, Fig. 2, comprising links 28, 33, 34, 35 and a self-levelling fluid suspension system, the system comprising a piston-cylinder unit 44, a hydropneumatic accumulator 45, 46, a source 50 of fluid pressure, a reservoir, and a valve spool 83, in a control valve 54, which places the chamber 44a of the unit in communication with the source or sink or isolates it, depending on the height of the unit, in response to movement of a height indicating linkage 155, 156 connected between the valve spool and one of the hitch links, the valve spool being releasably held by a detent (116, Fig. 3 not shown) so that there is lost motion at the linkage before height correction begins. This provides a "dead band" surrounding the mean height of the unit, to ensure that the levelling operation is not triggered by dynamic variations in the height of the unit, only by changes in the static load in the scraper. The height indicating linkage has a leaf spring 156. This may be arranged horizontally (Fig. 5 not shown) instead of vertically. Change in the height of the unit is accommodated by the leaf spring without movement of the valve spool until the force stored in the spring is sufficient to overcome the spring force holding a ball in a groove in the valve spool (Fig. 3). Parent Specification 1451329 has substantially the same disclosure, but claims a fluid suspension system with means for selectively connecting the normally vented rod chamber 44b to the chamber 44a to lower the piston. For Figures see next column