Motor-vehicle braking system having a vacuum-operated assistance device

A motor-vehicle braking system, having a vacuum-operated assistance device including a vacuum pump which is to be driven by a motor-vehicle engine, a fluid communication line between the vacuum pump and a chamber of said assistance device, for communicating a vacuum generated by said vacuum pump to said chamber, said braking system further comprising:

• a control valve, interposed along said fluid communication line, and having:
• a first operative condition, in which said control valve sets an inlet side of the vacuum pump in communication with the chamber,
• a second operative condition, in which the control valve sets the inlet side of the vacuum pump in communication with the atmosphere, and
• a one-way valve included within said control valve, which is operative when the control valve is in its first operative condition to enable a flow of air only in a direction which goes from said chamber towards the vacuum pump;
• a device for actuating the control valve, which is configured for:
• setting the control valve in its first operative condition, in which the inlet side of the vacuum pump communicates with said chamber, when the pressure within the chamber is above a predetermined threshold value, and
• setting the control valve in its second operative condition, in which the inlet side of the vacuum pump communicates with the atmosphere when the pressure within the chamber is below a predetermined threshold value;
• another one-way valve integrated into the vacuum pump and configured to prevent a flow of oil vapours from the vacuum pump towards the chamber;
• and
• an additional one-way valve integrated into the assistance device and configured to prevent a flow of air from the fluid communication line towards said chamber;
• wherein the control valve includes a valve member which is biased by a spring towards a first position corresponding to said first operative condition, in which the inlet side of the vacuum pump is in communication with the chamber, and
• wherein the valve member is directly exposed to pressure existing at a point along said fluid communication line between the chamber and the control valve, so that a vacuum existing in said chamber directly causes the valve member to move towards a second operative position, against an action of said spring, said second operative position corresponding to said second operative condition, in which the inlet side of the vacuum pump is in communication with the atmosphere.