Patent GB-1474988-A (GB)
Title: Two-circuit brake systems for motor vehicles
IPC: B60T15/04
Filed: 1974-08-23
Abstract: 1474988 Brake valves ROBERT BOSCH GmbH 23 Aug 1974 [27 Aug 1973] 37050/74 Heading F2F A driver-operated valve assembly 1 for a vehicle braking system has double-seat valves 10, 11 to control respectively the supply of compressed air between a supply connection 15 and a first working space 20<SP>1</SP> of a cylinder 2 of a brake master piston and cylinder actuating device and between a supply connection 17 and a second working space 24<SP>1</SP> of cylinder 2; the first valve 10 is operable by a thrust member 8 actuable by a brake pedal whilst the second valve 11 is operable by the action on a piston 19 of compressed air introduced into a chamber 34 when the first valve 10 is actuated or mechanically via a bolt 40 and a sleeve 29 if the pressure in the supply connection 15 should fail; the supply connection 15 incorporates a non-return valve 12 which closes in a direction towards a compressed air reservoir of the first supply connection 15 and thus acts to prevent all air being returned to the compressed air reservoir should the two spaces 20<SP>1</SP>, 24<SP>1</SP> be connected by seal failure as the valve assembly 1 is being operated. The cylinder 2 comprises a first working piston 20 slidable on a guide sleeve 23 and a second working piston 24 formed with a partially hollow piston rod 28 having a spherical end 28<SP>1</SP> which actuates the master cylinder piston. In operation of the assembly 1, the thrust member 8 is actuated to move, by way of a travel-limiting spring 30, a piston 31 which changes over valve 10 so that compressed air flows from the supply connection 15 to the working space 20<SP>1</SP> via a line 3. Pressure also builds up in the chamber 34 by way of a passage 33, and a control piston 19 is thereby moved against the force of a spring 19<SP>1</SP> to change over valve 11 so that compressed air flows from the supply connection 17 through an annular chamber 18 into a pressure change chamber 19<SP>11</SP> and then into working space 24<SP>1</SP> by line 3<SP>1</SP>. The spring 19<SP>1</SP> acts to create a lower pressure in chamber 19<SP>11</SP> than in chamber 34 when the pressures are in balance and since a higher pressure thus prevails in space 20<SP>1</SP> than in space 24<SP>1</SP> both working pistons 20, 24 are operated. If the supply connection 15 fails the control piston 19 is actuated mechanically by the bolt 40 and only space 24<SP>1</SP> will be pressurized. If connection 17 fails only space 20<SP>1</SP> will be pressurized and piston 20 will move to carry along piston 24. Should an 0-ring seal 42 on piston 20 fail, compressed air flows into space 24<SP>1</SP> at the commencement of braking and then flows to an outside air connection 16 by way of the second control valve 11 which is still open. Compressed air in the second circuit will be prevented from returning to the compressed air reservoir for the supply connection 15 by the valve 12. The piston 19 may have a double seal 9 with an intermediate chamber 9<SP>1</SP> connected to the outside air, which seal 9 acts to isolate chambers 34, 18. As an alternative to the double seal 1 a non- return valve 45 closing in a direction towards a compressed air reservoir for the supply connection 17 may be fitted upstream of the supply connection 17 to prevent compressed air flowing into this reservoir from the chamber 34 should a simple annular seal on piston 19 fail.