The accelerating uptake of electric buses, as operators throughout the UK work towards decarbonised fleets, has resulted in the introduction of new vehicle systems. These include the braking system, where engine-driven compressors have been replaced by standalone electric e-compressors. These provide compressed air for the braking system and power operated conventional parking brake systems, which are now being superseded by the Electronic Parking Brake (EPB) system.
Fitted as standard to the latest e-buses from manufacturers including BYD, Yutong and ADL/BYD, EPB replaces the spring-applied, air released park brake systems which have been fitted to buses and manually operated by drivers as standard practice for a number of decades. Developed for PSV applications by OEM suppliers including Knorr-Bremse and WABCO (ZF), EPB is connected to the vehicle’s Controller Area Network (CAN) and introduces electronic control and automatic park brake operation to provide enhanced safety and passenger comfort.
System overview
EPB operates as a standalone system and consists of two main components: The EPB pneumatic module (EPB-module), which controls the air pressure in the handbrake spring chambers and a Hand Control Unit (HCU). The EPB system controls the pressure in the pneumatically-connected spring brake chambers at the driver’s command, via the manually-operated HCU in the cab, as well as automatically.
Key EPB functions include automatic park and release and automatic hold to prevent vehicle rollaway, as well as gradual brake control, which combines EPB with the vehicle’s electronic braking system. EPB system information is provided via dashboard warning lamps to inform the driver of the system status:
- Amber warning lamp: Minor EPB failure, system can operate with reduced functionality
- Red stop lamp: Flashing warning signal in case of system failure
- EPB status lamp: Actuated when the parking brake is applied
Maintenance
For maintenance purposes, technicians can place the EPB system into a Workshop Mode which disables the automatic park brake function to allow inspection and servicing to be carried out. As EPB modules are vehicle-specific, replacement modules must be programmed to the particular vehicle in order for them to operate.
Fault diagnosis
As a leading supplier of OE bus components, including parts for the latest electric models, Imperial Engineering provides a range of diagnostic tools and software for PSV maintenance and repair. The Harlow based distributor has a wealth of bus brake system knowledge and is pleased to support operators with technical advice and guidance.
Photo used in this article courtesy of BYD Europe.
