Vehicle braking system distribution of front and rear braking forces is controlled according to two different distribution patterns depending upon vehicle load

A braking system of a diagonal or X-crossing type for braking a four-wheel motor vehicle by operation of a front and a rear brake for a front and a rear wheel of the vehicle, respectively, said braking system including two pressure application sub-systems which are connected to respective two mutually independent pressurizing chambers of a master cylinder, each of said two pressure application sub-systems comprising:

• (a) a front brake cylinder passage connecting a corresponding one of said two pressurizing chambers of said master cylinder and a front wheel brake cylinder of said front brake;
• (b) a rear brake cylinder passage connecting said front brake cylinder passage and a rear wheel brake cylinder of said rear brake;
• (c) a master cylinder cut valve in the form of a normally-open shut-off valve disposed in a portion of said front brake cylinder passage between said master cylinder and a point of connection of said front and rear brake cylinder passages, said master cylinder cut valve being closed when the braking system is in an anti-lock pressure control mode, and opened when the braking system is not in said anti-lock pressure control mode;
• (d) an intermediate valve in the form of a normally-open shut-off valve disposed in said rear brake cylinder passage;
• (e) a reservoir passage connected at one of opposite ends thereof to a portion of said rear brake cylinder passage between said intermediate valve and said rear wheel brake cylinder;
• (f) a reservoir connected to the other end of said reservoir passage;
• (g) a pressure reducing valve in the form of a normally-closed shut-off valve disposed in said reservoir passage;
• (h) a pump passage connected at one of opposite ends thereof to said reservoir and at the other end to a portion of said rear brake cylinder passage between said intermediate valve and a point of connection of said front and rear brake cylinder passages;
• (i) a pump disposed in said pump passage for delivering a working fluid from said reservoir to a portion of said each pressure application sub-system;
• (j) a controller operable in said anti-lock pressure control mode for controlling said master cylinder cut valve, said intermediate valve, said pressure reducing valve and said pump to effect an anti-lock pressure control operation for controlling pressures of said fluid in said front and rear wheel brake cylinders in an anti-lock manner;
• and
• (k) a check valve device disposed in a portion of said rear brake cylinder passage between the point of connection of said front and rear brake cylinder passages and a point of connection of said rear brake cylinder passage and said pump passage, said check valve device comprising a first check valve and a second check valve, said first check valve permitting a flow of the fluid therethrough in a first direction from said pump toward said front wheel brake cylinder after the pressure generated by the pump becomes higher than the pressure in said front wheel brake cylinder by more than a predetermined difference, and inhibiting a flow of the fluid therethrough in a second direction opposite to said first direction, said second check valve permitting a flow of the fluid therethrough in said second direction and inhibiting a flow of the fluid therethrough in said first direction.