Dual type hydraulic braking system for a vehicle

A dual type hydraulic braking system for vehicles, the system comprising, in combination;

• a master cylinder having two separate pressure chambers respectively associated with a first braking circuit and a second braking circuit, rear wheel cylinders and front wheel cylinders at respective front and rear vehicle wheels of a vehicle, and a pressure control valve assembly including a pressure control valve arranged between said master cylinder and at least one of said rear wheel cylinders in at least one of said braking circuits, said pressure control valve including a first piston for controlling braking pressure of said at least one rear wheel cylinder from a predetermined pressure of said master cylinder and including a second piston having a small diametered portion, a large diametered portion and a pressure receiving surface at an end surface thereof adjacent to said small diametered portion and which is coupled to and is affected by braking pressure in said second braking circuit, said second piston being biased by a spring acting against said braking pressure from said second circuit, said second piston being positioned to be moved by said spring into a first position in which control displacements of said first piston are restrained by said spring, wherein said second piston is positioned to be displaced by said braking pressure in said second braking circuit into a second position in which control displacements of said first piston are not restrained by said spring, spring force of said spring being larger than the force acting on said pressure receiving surface of said second piston when said braking pressure has reached a value at which the controlling operation of said first piston starts, and wherein among the five values;
• of (a) cross-sectional area (S.sub.3) of the small diametered portion of said second piston, (b) cross-sectional area (S.sub.4) of the larger diametered portion of said second piston, (c) the set load (F.sub.2) of said spring biasing said second piston, (d) starting pressure (P.sub.0) of the pressure control operation by said first piston and (e) predetermined pressure (P.sub.1) selected within a pressure range higher than said starting pressure, the following inequality can be established:
• P.sub.1 .multidot.(S.sub.4 -S.sub.3)>F.sub.2 >P.sub.0 .multidot.(S.sub.4 -S.sub.3),
• whereby, in case of both said circuits allowing normal pressure rising, said second piston moves in separating direction from said first piston after said first piston has begun the pressure controlling operation.

A dual type hydraulic braking system for vehicles, said system comprising a master cylinder having a first pressure chamber and a second pressure chamber respectively associated with a first braking circuit and a second braking circuit for separately delivering pressure of a same value thereto, rear wheel cylinders and front wheel cylinders at respective front and rear vehicle wheels of a vehicle, and a pressure control valve assembly including a pressure control valve arranged between said master cylinder and at least one of said rear wheel cylinders in said first braking circuit, said pressure control valve having a first piston which is biased by a first spring acting against the pressure delivered from said first pressure chamber for controlling braking pressure of said at least one rear wheel cylinder from a predetermined pressure P.sub.0 of said master cylinder and including a second piston having a small diametered portion and a large diametered portion with a pressure receiving surface at one end surface thereof adjacent to said small diametered portion, said pressure receiving surface being coupled to and affected by the pressure delivered from said second pressure chamber, said second piston being biased by a second spring acting against said pressure delivered from said second pressure chamber, said second piston being positioned to be moved by said second spring into a first position in which control displacements of said first piston are restrained by said second spring, said second piston being positioned to be displaced by said pressure delivered from said second pressure chamber into a second position in which control displacements of said first piston are not restrained by said second spring, spring force of said second spring being determined so that, in case of both said circuits allowing normal pressure rising, said second piston moves from said first position to said second position after said first piston has begun the pressure controlling operation resisting the spring forces of said first spring and said second spring.

A dual type hydraulic braking system for vehicles, said system comprising a master cylinder having a first pressure chamber and a second pressure chamber respectively associated with a first independent braking circuit and a second independent braking circuit for separately delivering pressure of a same value thereto, rear wheel cylinders at respective front and rear vehicle wheels of a vehicle, and a pressure control valve assembly including a pressure control valve arranged between said master cylinder and at least one of said rear wheel cylinders in said first braking circuit, said pressure control valve having a first piston which is biased by a first spring acting against the pressure delivered from said first pressure chamber for controlling braking pressure of said at least one rear wheel cylinder from a predetermined pressure P.sub.0 of said master cylinder and including a second piston having a small diametered portion and a large diametered portion with a pressure receiving surface at one end surface thereof adjacent to said small diametered portion, said pressure receiving surface being coupled to and affected by the pressure delivered from said second pressure chamber, said second piston being biased by a second spring acting against said pressure delivered from said second pressure chamber, said second piston being positioned to be moved by said second spring into a first position in which control displacements of said first piston are restrained by said second spring, said second piston being positioned to be displaced by said pressure delivered from said second pressure chamber into a second position in which control displacements of said first piston are not restrained by said second spring, spring force of said second spring being larger than the pressure force acting on said second piston when the pressure in said master cylinder has reached the value P.sub.0 and smaller than the pressure force acting on said second piston when the the pressure in said master cylinder has reached a value P.sub.2 which is higher than said value P.sub.0 and lower than the maximum value expected to be possibly generated in said master cylinder, sum of spring forces of said first spring and said second spring being smaller than sum of pressure forces acting on said first piston and said second piston when the pressure in said master cylinder has reached a value P.sub.1 which is larger than said value P.sub.0 and smaller than said value P.sub.2, whereby, in case of both said circuits allowing normal pressure rising, said second piston moves from said first position to said second position after said first piston has begun the pressure controlling operation.