Braking systems

A machine with a ground engaging structure by means of which the machine is drivable on the ground, the machine having a braking system including a brake actuator which is moveable by pressurized hydraulic fluid in a first direction, against a restoring force, to move a brake applying member to apply a braking force to a member to be braked, a master valve, including a piston assembly which upon operation of a brake operating member, directs the hydraulic fluid under pressure to the brake actuator to apply the brake, the system further including a source of pressurized hydraulic fluid, and a charging valve which is operable in first and second states, the piston assembly of the master valve including a pair of coupled pistons, and a chamber between the pair of pistons, the charging valve when operated in a first state communicating the source of pressurized hydraulic fluid to the chamber between the pair of pistons of the master valve, the coupling of the pistons permitting the pistons of the pair to move apart in response, up to a maximum distance thereby to direct up to a predetermined volume of hydraulic fluid to the brake actuator, to move the brake applying member in the first direction towards the member to be braked to reduce a running clearance between them, and the charging valve when operated in the second state, communicating the chamber to a lower pressure area to allow the pair of pistons to be moved towards one another, and thus to permit the brake actuator to move in a second direction opposite to the first direction to increase the running clearance between the brake applying member and the member to be braked.

A method of operating a braking system including a brake actuator which is moveable by pressurized hydraulic fluid in a first direction, against a restoring force, to move a brake applying member to apply a braking force to a member to be braked, a master valve, including a piston assembly which upon operation of a brake operating member, directs the hydraulic fluid under pressure to the brake actuator to apply the brake, the system further including a source of pressurized hydraulic fluid, and a charging valve which is operable in first and second states, the piston assembly of the master valve including a pair of coupled pistons, and a chamber between the pair of pistons, the charging valve when operated in a first state communicating the source of pressurized hydraulic fluid to the chamber between the pair of pistons of the master valve, the coupling of the pistons permitting the pistons of the pair to move apart in response, up to a maximum distance thereby to direct up to a predetermined volume of hydraulic fluid to the brake actuator, to move the brake applying member in the first direction towards the member to be braked to reduce a running clearance between them, and the charging valve when operated in the second state, communicating the chamber to a lower pressure area to allow the pair of pistons to be moved towards one another, and thus to permit the brake actuator to move in a second direction opposite to the first direction to increase the running clearance between the brake applying member and the member to be braked, the method including the steps of switching the operating state of the charging valve in response to varying operating parameters of a machine in which the braking system is incorporated.