A metro vehicle or driverless system generally consists of several car bodies. We will look at the hydraulic braking system of a single car body with two bogies.
Each bogie is equipped with a spring-applied brake caliper HYS 257 per axle. HYS 257 is a floating mounted “one-cartridge brake caliper” with direct impact. The brake caliper is directly attached to the axle bearing via a bracket and acts on an internally vented axle-mounted brake disc. Each bogie has two independent hydraulic circuits: a service circuit and an auxiliary circuit for potential malfunctions. An electro-hydraulic module (EHM) positioned underneath the car body performs proportional, hydraulic activation of the spring-applied brake calipers on individual bogie basis. The modular, ready-to-install, electrohy-draulic module contains the entire hydraulic brake activation equipment, consisting of hydraulic pressure generation, pressure regulation and electric brake control. All components are electrically controlled and monitored via three independent brake control units of type HEY-C which are integrated into the EHM module. Braking and electric control functions performed by the EHM module:
- Service brake, emergency brake and parking brake
- Wheel-slide protection, load registration, blending, diagnosis and monitoring
In the event of a malfunction of the main hydraulic system, the spring-applied actuators of both bogies can be released by a separate auxiliary hydraulic power unit via an independent hydraulic circuit. A second manual auxiliary release possibility is provided by a transportable hand pump via a ball valve which is integrated between auxiliary hydraulic power unit and spring-applied actuators. To increase deceleration in emergency and safety braking, both bogies have track brakes.