Patent GB-973737-A (GB)
Title: Improvements in or relating to braking apparatus for trailer vehicles
IPC: B60T11/10
Filed: 1961-09-13
Abstract: 973,737. Brakes for trailer vehicles. H. P. HENRY. Dec. 13, 1962 [Sept. 13, 1961], No. 32857/61. Headings F2E and F2F. A brake for a trailer vehicle comprises a housing 11 on the trailer vehicle in which slides a member 13 adapted to operate the piston 28 of a master cylinder 18 secured to and extending within the housing, a coupling 14 being provided on the member 13 for attachment to a tractor vehicle whereby the master cylinder is operated by overrunning of the tractor vehicle by the trailer vehicle, means for moving member 13 to operate the piston 28 when the trailer vehicle breaks away from the tractor vehicle, and pawl-and-ratchet mechanism which is rendered operative by the operation of the means so that the brakes are held applied only after operation by the means. The operating means may be either a ground engaging sprag or a chain(s) connecting tractor and trailer, or, as shown, both. In the embodiment of Figs. 1 and 5, the sprag comprises pair of lever arms 33 slotted at 36 to engage a pivot pin 31 and having also a pin-and-slot connection 37, 39 with the member 13. The pin 39 carries a roller 38. A pawl 41 is pivoted at 44 to the upper end of the lever arms is held out of engagement with a rack 40 carried by the housing 11 by means of a strut 46 connected between pin 31 and a shear pin 47 extending through the pawl 41 and the adjacent arm 33. A chain 51 extends between a point on the tractor vehicle and a plate 42 secured to the pawl, and an extension chain 53 is connected between the latter and a fixed anchorage 54 on the trailer. In normal operation the shear pin 47 holds the pawl 41 out of contact with the rack 40 and braking is effected only when the trailer vehicle approaches the tractor vehicle causing sliding of the member 13 in the housing 11 to operate the piston 28. This movement is damped by a damper comprising an enlargement 15 on the member 13 acting on braking fluid supplied to a chamber 21 from the brake reservoir 25 via seals 26 acting as non-return valves, movement in either direction causing fluid to be forced through one or other of two restrictions 22, 23 communicating with a bore 24 in member 13 which returns the fluid to the reservoir. When the coupling 14 parts the lower ends 34 of the sprag arms 33 engage the ground, studs 35 biting into the ground to cause them to grip so that pressure is exerted rearwardly via the connection 37, 39 on the member 13 to apply the brake strongly. At the same time the impact of ends 34 with the ground breaks shear pin 47 to allow pawl 41 to drop on to the rack 40 and lock the brake on. Chain 51 becomes taut and also assists both in applying the brake and lowering the pawl. Manual operation of the brake for parking is effected by a hand-lever 49 pivoted at 50 to housing 11 and connected via a compressible link 48 to the pivot 44. The arrangement is such that when lever 49 is moved fully in the direction of the arrow the connection between it and the link 48 passes over-centre to lock the lever. In a modification, Fig. 6, the sprag arms 56 are similarly arranged with respect to sliding member and coupling 55 but the strut 46 and shear pin 47 are replaced by a spring 67 which is normally tightly coiled to act as a strut between the pivot pin 58 mounting the sprag arms and pin 68 carried by a pawl 62 so that the pawl is out of contact with a rack 63 secured to housing 59. When the trailer breaks away and the sprag arms hit the ground pin 58 travels to the lower end of slots 57 in the sprag arms so that spring 67 is tensioned to move the pawl into engagement with the rack. The tensioning of the spring 67 also exerts a camming force downwardly via inclined edge 69 of the pin-and-slot connection 60, 61 with the member 55, so as to augment the brake applying force on the member 55. Reference has been directed by the Comptroller to Specification 807,100.