Electric Bus

Overview

The electric bus is a battery-powered version of the 12 m low-floor city transit bus. It carries a lithium traction battery of 350-550 kWh that feeds an AC traction motor of 150-250 kW through an inverter, replacing the diesel engine and gearbox of a conventional bus. The vehicle is charged either at the depot through a plug-in CCS inlet at up to 150 kW or en-route through a roof pantograph at 300-600 kW. A typical city duty cycle of 200-350 km per day is covered by depot charging overnight, while high-utilisation routes use opportunity charging at terminals to top up during layovers.

The body keeps the stepless low floor of a modern city bus, with an entrance height of 320-340 mm and a flat aisle made possible by a portal rear axle. Batteries sit on the roof and in the rear engine bay, which keeps the passenger compartment unobstructed and lowers the centre of gravity compared with floor-mounted packs. The Traction Battery System and Traction Drive are the two largest subsystems by value, followed by the Charging System and the HVAC System unit, which on an electric bus draws from the traction battery rather than from engine waste heat.

Traction battery system

The Traction Battery System is split into roughly six roof-mounted enclosures. Each Battery Pack is a sealed IP67 housing of about 60-90 kWh holding eight Cell Module units, a Slave BMS Board board, two HV Contactor units, an HV Pack Fuse and a Pack Current Sensor. A module clamps 24 Prismatic Lithium Cell units between two Module End Plate plates with Cell Interconnect Busbar welds and a Cell Balance Harness running to the slave board. LFP cells give long cycle life and tolerate full charging, while NMC cells give higher energy density where range matters more than calendar life.

Cell temperature is held in a 15-35 °C window by an Battery Cold Plate bonded under each pack, fed by two Coolant Pump units circulating water-glycol. The Master BMS Controller controller aggregates per-cell voltage and temperature from each Slave BMS Board, computes state of charge and state of health, and commands the HV Contactor units through a pre-charge sequence. All packs connect through the HV Junction Box, which carries the Main HV Fuse, a Manual Service Disconnect for safe maintenance and the HV Distribution Busbar distribution. Orange HV Cable Set runs link the battery to the inverter, charger and DC-DC converter.

Traction drive

The Traction Drive uses a single Traction Motor, either an interior-permanent-magnet machine for efficiency or a rugged induction machine. The motor is built around a Stator Assembly and a Rotor Assembly running on two Ball Bearing units with Oil Seal seals in an Motor Housing water jacket, and a Rotor Position Resolver reports rotor angle for field-oriented control. The Traction Inverter converts battery DC to variable-frequency AC using six IGBT Power Module half-bridges, an DC-Link Capacitor bank, three Gate Driver Board boards and an Inverter Control Board running the torque loop, all cooled by an Inverter Cold Plate.

Drive reaches the rear wheels through the Reduction Gearbox, a single-speed unit of about 10:1 built from two Helical Gear Pair stages in a Gearbox Housing on four Ball Bearing units, with an Differential splitting torque between the wheels. During braking the same motor runs as a generator, returning energy to the battery; this regenerative braking recovers a large share of the kinetic energy lost at every stop, which is why a stop-start city duty cycle suits battery buses well. The Drive Coolant Pump shares the cooling loop with the inverter.

Charging and energy management

Depot charging uses the CCS Charge Inlet, a CCS Combo 2 inlet with an Charge Inlet Housing, a Charge Pin Set, an Inlet Lock Actuator and Inlet Temperature Sensor units. Opportunity charging uses the Charging Pantograph, whose Pantograph Arm and Pantograph Head are raised by an Pantograph Actuator to meet an overhead mast, with Contact Strip strips held against the busbars by Coil Spring force. The Charge Controller negotiates the charging session and supervises current and isolation, while the DC-DC Converter steps the high voltage down to 24 V for the auxiliary system through an DC-DC Transformer.

Body, running gear and braking

The Body Shell is a welded space-frame Skeleton Frame with a low Floor Structure, bonded Side Wall Panel and Roof Panel skins, a composite Front Mask and Rear Mask, a laminated Windscreen and bonded Side Window. The Running Gear carries a steerable Front Steer Axle and a portal Rear Drive Axle whose Portal Hub Reduction gears clear the central aisle. The Air Suspension uses six Air Spring Bellows and six Shock Absorber units, levelled by Levelling Valve valves and supplied by an Air Compressor feeding two Air Reservoir tanks; kneeling lowers the entrance at each stop. The Steering Gear uses an Steering Box with an electric Steering Pump.

The Brake System blends regenerative braking with dual-circuit pneumatic disc brakes. Each wheel has an Brake Disc and an Brake Caliper applied by an Spring Brake Chamber spring actuator. The EBS Control Module meters how much retardation the motor provides and how much the friction brakes add, so the pads wear slowly; Wheel Speed Sensor units feed wheel speed and an Air Dryer protects the pneumatics.

Auxiliary electrics, climate and cabin

The Low-Voltage Electrics system runs at 24 V from two Auxiliary Battery units kept charged by the DC-DC converter. The Vehicle Control Unit coordinates drive, charging and body functions over CAN, the Power Distribution Box box feeds the loads, and lighting uses LED Headlamp, LED Tail Lamp and Saloon Light LED units plus an Destination Sign. The HVAC System system is a roof heat-pump unit with an HVAC Compressor, an Condenser Coil, Evaporator Coil coils, HVAC Blower blowers and an PTC Heater for cold-weather backup, all under an HVAC Controller. Heating is the largest auxiliary load and the main range penalty in winter.

The Passenger Cabin seats 28 or more on Passenger Seat units, with three Door System plug-sliding doors driven by an Door Drive Unit, Grab Rail stanchions, Interior Trim Panel trim, an Driver Area workstation and an Wheelchair Ramp for step-free boarding.