Patent GB-1268339-A (GB)
Title: An automotive wheel brake unit
Inventor: NYUNOYA MIZUO
IPC: F16D65/22
Filed: 1970-12-29
Abstract: 1,268,339. Manual/power shoe drum brakes; inactivating the slack adjuster. AISIN SEIKI K.K. 29 Dec., 1970 [25 Dec., 1969], No. 61623/70. Heading F2E. An internal shoe drum brake which includes a hydraulic actuator, a parking-brake lever actuator in proximity to the hydraulic actuator and an automatic slack adjuster, has means for disabling the slack adjuster during hydraulic actuation and for permitting the slack adjuster to perform its normal operation (when required) during "parking-brake" actuation. As shown in Figs. 1 and 2 a member 56 having a U-shaped recess 58<SP>1</SP> is located on the end of one of the pistons 12 of a conventional two-piston hydraulic actuator 11 incorporating a compression spring 59 between the pistons. The two vertical faces of member 56 are normally in contact with the piston and the edge of the brake shoe 15 respectively, while the recess 58<SP>1</SP> engages the vertical part of a pawl lever 25 pivoted at 23 to the shoe 15. A parking or hand brake lever 49 is also pivoted directly at 23 on the shoe 15, but between lever 49 and pawl lever 25 a spacer 63<SP>1</SP> is located to allow for the intervening part of member 56. A spring 39 is located between a pin 38 on pawl lever 25 and a pin 55 on the main body 33 of an adjustable strut 26. The main body 33 has external threads, (not shown), co-operating with internal threads in a ratchet wheel 31, the wheel 31 being rotatable by the resilient end of pawl lever 25 in a certain situation. Grooves 50 and 52 at the ends of the strut 26 engage grooves 51 and 53 at the upper ends of shoes 14 and 15 respectively, while groove 52 also engages edge 54<SP>1</SP> of "parking brake" lever 49. The lower end 29 of pawl lever 25 can make contact with a shoulder 28 on the main body 33.  In operation, when the shoes are hydraulically actuated, member 56 prevents pawl lever 25 from pivoting about 23, and thereby prevents operation of the slack-adjusting mechanism of strut 26; spring 39 expands slightly. When, instead, the shoes are operated by cable 63 via the "parking brake" lever 49, strut 26 is urged to the left by its engagement with lever 49, (a compression spring 54 being located between strut 26 and shoe 14), and spring 39 rotates pawl lever 25 clockwise slightly. If the gap between shoe and drum is excessive, pawl lever 25 rotates ratchet wheel 31. Spring 59, being relatively weak, permits this action. When parking brake application follows, or is simultaneous with, hydraulic application, member 56 again prevents rotation of pawl lever 25, and, again, no slack adjusting takes place. In Fig. 4, the pawl lever 25<SP>1</SP> is is shaped and arranged for counter-clockwise actuation of ratchet wheel 31. It is pivoted by pin 23<SP>1</SP> on the main body 33 of strut 26 instead of on the shoe 15, and spring 39<SP>1</SP> extends in this case between pin 38 on the pawl lever and a pin 71 on the shoe 15. A motion-transmission lever 69 has slotted engagement with pin 38 and pivotting engagement with pin 71. In either case, because slack-adjustment is prevented during hydraulic actuation; spurious slack adjustment resulting from thermal and/or mechanical deformation of the drum during hydraulic actuation is avoided also. Minor variants.-In the embodiment of Figs. 1 and 2 one of the pistons may be rigid with backing plate 10 and the cylinder axially slidable on the plate; a similar arrangement may be adopted for the embodiment of Fig. 4.