Patent GB-1149680-A (GB)
Title: Improvements in or relating to brakes for motor vehicles
IPC: B60T13/58
Filed: 1967-06-09
Abstract: 1,149,680. Vehicle braking systems. ROBERT BOSCH G.m.b.H. 9 June, 1967 [11 June, 1966], No. 26714/67. Heading F2F. A vehicle braking system comprises a compressed air assisted hydraulic main brake and an auxiliary brake controlled from a compressed air source through an emergency brake valve and a spring- loaded brake cylinder, the emergency brake valve having a closure member which is biased closed by the pneumatic pressure and biased open by the hydraulic pressure so that the brake cylinder is vented to the atmosphere if the hydraulic pressure fails when the main brake lever is actuated. The system shown in Fig. 2 comprises main brakes 10, 11 operated from an hydraulic master cylinder 8 and pedal 6, boosted by compressed air from a compressor 1 and reservoir 4<SP>1</SP>. An auxiliary brake 17 is operated by a cylinder 15 normally under air pressure, but if the air pressure falls to atmospheric the auxiliary brake is applied by a spring in the cylinder 15. The system also provides for braking a trailer via lines 59 and 74. Normal operation.-When braking normally by the pedal 6, the emergency brake valve 13 is inoperative, a hollow valve stem 27 being urged upwards by the hydraulic pressure of the main brakes acting through line 43 on a piston 42 and being urged downwards by the pneumatic pressure through lines 36, 58, 79 acting on a piston 29. The space 39 between these pistons is permanently vented to the atmosphere. The trailer brakes are applied via an auxiliary valve comprising two valve stems 61, 81 in separate chambers. The pneumatic pressure in the main brake booster 7 is applied via lines 36, 58, 59 to the trailer brakes, the auxiliary valve not operating. The hydraulic pressure in the main brake system urges a piston 82 upwards, but this is counteracted by the downward force on a piston 80 by the pneumatic pressure in chamber 77 through lines 79, 78, so that the valve stem 81 does not move. Similarly, on the valve stem 61, a piston 62 is urged upwards by the pneumatic pressure applied through opening 63 to the chamber 64, but is urged downwards by a balance beam 85 whose other end is attached to the valve stem 81. Braking by hand brake.-When the lever 38 is operated, compressed air from reservoir 4<SP>11</SP> is admitted to chamber 91, urging piston 90 upwards. By linkage 92-94, valve stem 81 is pushed upwards and valve stem 61 downwards, so that valve 60 rests on seating 56 and cuts off line 58 from the booster 7. The valve stem 81 lifts valve 75 from its seat 76 so that compressed air flows through line 12 and chamber 21 to chamber 70 and thence into chambers 77 and 33, and into line 74 to operate the trailer brakes. The pressure in chamber 33 urges piston 29 downwards so that valve 20 abuts the seat 24 and the top of the hollow stem 27 is unsealed. The cylinder 15 is then vented to the atmosphere through line 14, chamber 26, valve stem 27 and opening 40. The pressure in chamber 30 acting on piston 28 is ineffective since piston 29 is of larger area. When the hand brake is released, the pneumatic pressure on piston 80 and the force of the springs 65, 89 return the valve stems to their original positions, the pressure in chambers 33 and 77 being relieved via line 36 and the open valve of the booster 7. failure of hydraulic system.-Operation of pedal 6 builds up a pressure in the booster 7 which applies pneumatic pressure via line 36 to chamber 33 and to line 59 to operate the trailer brakes. The pressure in chamber 33 forces piston 29 downwards and vents cylinder 15 as above to operate the auxiliary brake. Failure of pressure in booster 7 or line 36.- Operation of pedal 6 builds up hydraulic pressure in line 9 to operate the main brakes directly. This urges piston 82 upwards and moves the valve stems 61, 81 into their operative positions to apply the trailer brakes as for hand brake operation. The effect of the pneumatic pressure on piston 29 outweighs the hydraulic pressure on piston 42 since the latter is of smaller area. Failure of pressure in reservoir 4<SP>11</SP>.-The absence of pressure in cylinder 15 causes the spring therein to apply the emergency brakes. Operation of pedal 6 causes the hydraulic pressure to lift piston 82 and valve stem 81 until the latter presses the valve 75 against a ring 72. Pressure in line 74 then falls while that in line 59 rises, and a control valve on the trailer responds to apply the brakes. Failure of trailer line 59.-Pressure in line 74 is vented through the break in line 59 and the trailer control valve responds as before. Modifications.-The hand brake may be mechanical, in which case the lever 93 is attached to the hand brake linkage instead of piston 90. The hydraulic circuit can be split into two parts, for front and rear axles respectively, the auxiliary valve being connected to the rear axle circuit. A simpler system for use without a trailer is also described (Fig. 1, not shown).