Vehicle brake system having a brake pedal unit

A brake pedal unit connected to a brake pedal and in selective fluid communication with a fluid reservoir, the brake pedal unit comprising:

• a housing defining a bore formed therein;
• an input piston slidably disposed in the bore, wherein the input piston is connected to the brake pedal such that engagement of the brake pedal causes movement of the input piston within the bore of the housing of the brake pedal unit, and wherein the brake pedal unit is defined to be in an at rest position when the brake pedal in not engaged causing movement of the input piston, movement of the input piston pressurizing an input chamber in selective fluid communication with a pedal simulator;
• an input passageway permitting fluid communication between the input chamber and the reservoir when the brake pedal unit is in the rest position;
• a primary piston slidably disposed in the bore for pressurizing a primary chamber;
• a primary passageway permitting fluid communication between the primary chamber and the reservoir, wherein fluid flow through the primary passageway is blocked when the brake pedal unit is in the rest position;
• a secondary piston slidably disposed in the bore for pressurizing a secondary chamber;
• and
• a secondary passageway permitting fluid communication between the secondary chamber and the reservoir, wherein fluid flow through the secondary passageway is blocked when the brake pedal unit is in the rest position;
• when the brake pedal unit is in the rest position, the fluid communication between the primary chamber and the reservoir is blocked via the blocked primary passageway, the fluid communication between the secondary chamber and the reservoir is blocked via the blocked secondary passageway, and the input chamber and the reservoir are in fluid communication via the input passageway, and
• during a normal manual push through event in which the brake pedal is depressed, the fluid communication between the primary chamber and the reservoir is blocked via the blocked primary passageway, the fluid communication between the secondary chamber and the reservoir is blocked via the blocked secondary passageway, fluid flow through the input passageway is blocked, and the fluid communication between the input chamber and the reservoir is blocked via the blocked input passageway.