GB1397795A - Bumper bar assembly for motor vehicles - Google Patents

Abstract

1397795 Bumpers FICHTEL & SACHS AG 12 May 1972 [15 May 1971] 22448/72 Heading B7J [Also in Division F2] A bumper bar assembly for motor vehicles comprises at least one shock absorber acting on a bumper bar, the or each shock absorber comprising a piston-rod 2, Fig. 2, extending into a liquid-filled cylinder 1 and carrying a piston 3 affixed thereto by riveting at pin 13, the piston 3 separating two liquid chambers, one shown at 16 and the second defined between piston 3 and a displaceable boundary surface formed by an annular piston 5 floating on the rod 2 against the elastic resistance of a spring 7 (and being of negligible size as shown in the extended position of the shock absorber prior to an impact). On impact, piston 3 is moved by rod 2 away from piston 5 while liquid flows through throttled passage means formed by grooves 4 in the inner surface of the cylinder wall, into the second chamber, and the boundary surface formed by the floating piston 5 is displaced so as to modify the total volume of the two liquid chambers in response to the change in immersion volume of rod 2, the throttling effect of the passage means 4 being such that, after an initial increase, the force provided by the shock absorber remains approximately constant throughout the remainder of the piston stroke. The grooves 4 as shown are rectilinear and have straight, tapering sides and are of uniform depth, but they may be of various shapes such as curved grooves, or grooves 604, Fig. 6, of constant width, and depth varying parabolically in the longitudinal direction. In Fig. 6, a protective tube 622 is provided surrounding part of cylinder 601 and having a base 642, which carries the end of piston-rod 602 and which also acts as the base of an attachment part 640 having transverse apertures 644 to receive a securing pin for attachment to the bumper bar or a vehicle body. As an alternative to grooves in the cylinder wall, such as in Fig. 9 the passage means between the two liquid chambers may be formed by borings 950 in piston 903 which are normally covered by a valve plate 948 under the action of spring washers 947. On another form, Fig. 4, the piston-rod 425 is a hollow tube sealed at the piston by a plate 426. Further, as in Fig. 9, the floating piston 905 may be located within the rod 902 and the elastic resistance to its movement be supplied by a cushion of gas 955 instead of a helical spring. Other forms of valve to control passage means comprising borings in the piston are described with reference to Figs. 12- 16 (not shown).