Vehicle braking system with booster arrangement

1. A boost arrangement for pressurizing a master cylinder of a vehicle braking system of a vehicle, the boost arrangement comprising:

a housing defining a boost chamber filled with brake fluid and in fluid communication with a reservoir of brake fluid;

the boost chamber having a first portion and a second portion, the second portion being generally axially aligned with a driver input rod, wherein the driver input rod is linearly moveable and operatively coupled to a driver brake pedal of the vehicle, the first portion being spaced apart from and axially unaligned with the second portion, but in fluid communication with the second portion;

a primary piston at least partially disposed in the first portion of the boost chamber, the primary piston defining an opening extending straight therethrough from a first end of the primary piston to an opposing second end of the primary piston; and

a secondary piston having a distal end extending into the opening defined by the primary piston and a proximal end outside the housing;

both of the primary piston and the secondary piston being disposed within the first portion of the boost chamber and movable along an axis which is axially unaligned with the driver input rod; and

wherein the boost arrangement actuates the master cylinder to operate a friction braking arrangement of the vehicle.

2. The boost arrangement of claim 1 , wherein the primary piston is tubular.

3. The boost arrangement of claim 1 , wherein the primary and secondary pistons cooperate to displace a tubular area of brake fluid in response to movement of the primary piston from a first position to a second position.

4. The boost arrangement of claim 1 , wherein the primary and secondary pistons are independently movable relative to the housing.

5. The boost arrangement of claim 1 , wherein the housing includes an input port open to the first portion of the boost chamber and in fluid communication with the reservoir of brake fluid, and wherein the primary piston is movable from a first position and second position for closing the input port.

6. The boost arrangement of claim 1 , wherein the secondary piston extends completely through the primary piston.

7. The boost arrangement of claim 1 , wherein the secondary piston includes a second end directly opposed by a biasing member.

8. The boost arrangement of claim 1 , wherein the secondary piston is driven through a first range of motion without displacing the primary piston and driven through a second, further range of motion in which the primary piston is displaced.

9. A braking system for a vehicle, the vehicle including a hydraulic brake device for applying a friction brake force to at least one wheel of the vehicle, the braking system comprising:

a master cylinder in fluid communication with a reservoir of brake fluid and in fluid communication with the hydraulic brake device; and

an electric brake force generator for moving brake fluid within the master cylinder to deliver brake fluid to the hydraulic brake device in response to a first predetermined displacement of a brake pedal, the electric brake force generator including a housing defining a boost chamber filled with brake fluid and in fluid communication with the reservoir of brake fluid;

the boost chamber having a first portion and a second portion, the second portion being generally axially aligned with a driver input rod, wherein the driver input rod is linearly moveable and operatively coupled to a driver brake pedal of the vehicle, the first portion being spaced apart and axially unaligned with the second portion, but in fluid communication with the second portion;

the electric brake force generator further including a primary piston and a secondary piston that cooperate to displace brake fluid in response to movement of the primary piston from a first position and a second position, the secondary piston extendable completely through an opening passing through the primary piston;

both of the primary piston and the secondary piston being disposed within the first portion of the boost chamber and movable along an axis which is axially unaligned with the driver input rod, the secondary piston having a proximal end outside the housing; and

wherein displacement of brake fluid from the boost chamber actuates the master cylinder to operate the hydraulic brake device.

10. The braking system of claim 9 , wherein the primary and secondary pistons are independently movable relative to the housing and relative to the driver input rod.

11. The braking system of claim 9 , wherein the housing of the boost chamber includes an input port in the first portion which is in fluid communication with the reservoir of brake fluid, and wherein the primary piston is movable from the first position and the second position for closing the input port.

12. The braking system of claim 9 , further comprising a biasing member disposed in the chamber and biasing the primary piston toward the first position.

13. The braking system of claim 9 , wherein the braking system is operative in a first mode when the primary piston is in the first position and a second mode when the primary piston is in the second position.

14. The braking system of claim 9 , wherein the secondary piston is driven through a first range of motion without displacing the primary piston and driven through a second, further range of motion in which the primary piston is displaced.