Patent GB-1503080-A (GB)
Title: Combination of a slack adjuster and a brake unit for a rail vehicle
IPC: F16D65/56
Filed: 1976-07-12
Abstract: 1503080 Slack adjusters SAB INDUSTRI AB 12 July 1976 [14 July 1975] 28852/76 Heading F2E A combination of an automatic slack adjuster and a cylinder-and-piston brake unit for a rail vehicle brake system comprises a housing 1, a piston tube 6 attached to the piston 4 of the unit, a non-rotatable spindle 7 coaxial with tube 6 and displaceable therein to actuate a brake, a nut 9 in non-self-locking screw-thread engagement with the spindle, two (preferably toothed) clutch surfaces 9<SP>1</SP>, 9<SP>11</SP> on the nut 9 for respective co-operation with (preferably toothed) clutch surfaces 6<SP>1</SP>, 6<SP>11</SP> on the piston tube 6 the spacing of surfaces 9<SP>1</SP>, 9<SP>11</SP> being different from the spacing of surfaces 6<SP>1</SP>, 6<SP>11</SP>; a spring 14 is arranged between a fore control means 12 and a rear control means 13 and when the combination is in a brake-released rest position the fore control means 12 is behind a housing fore shoulder 16 at a distance A corresponding to the desired slack and coacts with a nut fore shoulder 10, and the rear control means 13 is then in front of a nut rear shoulder 11 at distance A and coacts with a housing rear shoulder 17. The combination illustrated in Fig. 1 has piston 4 operable by fluid pressure admitted through an inlet 3. The shoulders 16, 17 are formed on a control sleeve 15 screw-threaded within housing 1 and adjustable relative thereto to alter the distance A. The control means 12, 13 are of annular sheet metal form and the shoulders 10, 11 are constituted by thrust bearings although they could be constituted by plain collars for example. A spindle piston 19 is attached to spindle 7 and is sealed relative to piston tube 6 so that fluid pressure admitted through inlet 3 acts on piston 19 as well as piston 4. A check valve 20-23 ensures that the maximum fluid pressure remains acting on piston 19 even after the fluid pressure acting on piston 4 has decreased. If during brake actuation the brake appli. cation stroke is too short or too long the nut 9 will be rotated under the influence of spring 14 to bring the brake application stroke to the desired magnitude corresponding to distance A. If the brake application stroke is too short then spindle 7 operable by pressure on spindle piston 19 is prevented from following the continuing displacement of piston 4 and tube 6, so that clutch 6<SP>1</SP>, 9<SP>1</SP> is disengaged to allow nut 9 to rotate until fore control means 12 reaches shoulder 16 and bearing 11 reaches rear control means 13. During further operation in the "elasticity" part of the brake application stroke fore clutch 6<SP>1</SP>, 9<SP>1</SP> will disengage and rear clutch 6<SP>11</SP>, 9<SP>11</SP> will engage and the force from the piston tube 6 will be transmitted via clutch 6<SP>11</SP>, 9<SP>11</SP> to nut 9 and spindle 7. Decreasing fluid pressure allows the return or release stroke to commence. If the brake application stroke is too long and assuming that the pressure trapped by check valve 20-23 from a previous application and acting on piston 19 is sufficient to overcome the friction forces in the brake rigging during brake application, then during the application stroke bearing 10 will leave control means 12 and control means 13 will be lifted from shoulder 17, clutch 6<SP>1</SP>, 9<SP>1</SP> will be disengaged and nut 9 will rotate on spindle 7. If the aforesaid pressure is insufficient to overcome the friction then adjustment takes place during the return stroke. In the modified construction of Fig. 2 (not shown) the nut (39) is extended rearwardly rather than forwardly as in Fig. I. In the embodiment of Fig. 3 (not shown) the nut (69) consists of two coaxial parts of which the inner one is screw-threaded and the outer one is an extension with the thrust bearings (70, 71). Also there is no check valve for the spindle piston (79) as illustrated, although such could be provided, further Figs. 1, 2, may have no check valve. A mechanical means may be provided to open the check valve to allow the spindle 7 to be retracted manually. The slack adjuster may be made single-acting instead of double-acting by transforming bearing 10 into a non-rotating part. A spring arrangement to load the spindle may replace the piston 19. In a further modification there may be inwardly directed clutch surfaces on the nut at a greater axial distance from each other than complementary outwardly directed clutch surfaces on the piston tube.