Volvo 7900 Hybrid

Volvo 7900 Hybrid
SBS Transit Volvo 7900 Hybrid
Volvo 7900 Hybrid
Manufacturer Volvo Buses
Bodywork Wrightbus (TBC)
Years in operation 2H 2018–
Operators To Be Announced
Technical Data
Length 12.0 metre
Engine Volvo D5K 240
Transmission Volvo AT2412E I-Shift
Accessibility Low Floor & Wheelchair-accessible
Emission Standard Euro VI  (EGRSCR)

The Volvo 7900 Hybrid is a low-floor, single-deck, diesel-hybrid city bus built by Volvo Buses for the European market. Part of the Volvo 7900 family of buses, the Volvo 7900 Hybrid offered as an integral product (i.e. completely-built-up) and assembled in Wroclaw, Poland.

50 units of the Volvo 7900 Hybrid bus were procured by the Land Transport Authority in 2017 as part of efforts to build a more environmentally friendly public bus fleet. These buses are expected to enter service starting from the second half of 2018. Read more about the procurement process here.

European bus operators are primary customers of the Volvo 7900 with many operating in the United Kingdom, Sweden, Spain, Germany, Switzerland, Norway, Estonia, Poland, as well as Colombia.

Background Information:

The Volvo 7900 range of buses was produced by Volvo Buses since 2011, when it was initially offered with a Euro V/EEV diesel or CNG engine in both rigid and articulated bus variants. The Euro VI engine range was offered starting from 2013. 

As its name implies, the Volvo 7900 Hybrid runs on both diesel and electricity (more specifically, a parallel hybrid drivetrain), which achieves up to 39% fuel savings and reducing NOx/PM emissions by almost to 50%. By using electricity to power the bus during periods of high energy demand, less strain is put on the combustion engine, hence lowering fuel consumption and emissions.

The standard 12-metre Volvo 7900 Hybrid variant is available in both LHD and RHD models, with an early 10.6-metre model since discontinued. A current 18.0-metre articulated variant, the Volvo 7900 Hybrid Articulated, is also offered.

Two newer propulsion systems have been developed for the Volvo 7900. The Volvo 7900 Electric Hybrid, launched in 2014, is an improved hybrid bus designed to run mainly in electric mode. The Volvo 7900 Electric, launched in October 2017, is a fully-electric bus solely powered by electric motors. Both versions are complemented with Volvo’s Opportunity Charging System, a rapid charging station at the end stations of a bus route that quickly tops up a vehicle’s battery via overhead catenary. 

Hybrid System:

In the Volvo 7900 Hybrid, electricity is generated during cruising and regenerative braking, and stored in lithium-ion battery cells. The energy in the batteries is released to assist the engine in powering the vehicle. Hence, the engine is less strained while accelerating or going up hills, reducing fuel consumption.

The Volvo Hybrid Driveline is the core of the parallel hybrid system, comprising of four main components: the Euro VI diesel engine, the I-SAM motor, the automated gearbox and the energy storage system. The Integrated Starter Alternator Motor (I-SAM) is key to the hybrid process, combining a motor/generator with a Powertrain Control Unit and a DC/AC Power Electronic Converter (PEC) to convert the electrical energy into mechanical energy and vice versa in-between periods of motoring and regenerative braking.

In a parallel hybrid drivetrain, the combustion engine and the electric motor are connected to the transmission independently. During periods of high energy demand, both the electric motor and the combustion engine power the transmission This differs from a series hybrid drivetrain, where the bus is propelled exclusively by the electric motor, and the internal combustion engine is connected to an electric generator which converts the energy produced by the internal combustion engine into electric power for the motors.

Volvo 7900 Hybrid Driveline
Volvo 7900 Hybrid Driveline
See Also: Volvo Diesel Hybrid Buses procured by LTA

Volvo 7900 Hybrid:

These buses have yet to be delivered.

Basic Technical Specifications
Engine Volvo D5K 240, 5.1-litre
Power/torque rating of 240hp (177 kW) @ 2200 rpm | 918Nm @ 1200-1600 rpm
Emissions control Euro VI-compliant
Engine combines Exhaust Gas Recirculation (EGR) with Selective Catalytic Reduction (SCR), hence requiring diesel exhaust fluids such as AdBlue
Motor / Battery Volvo I-SAM Electric Motor, paired with Li-Ion batteries
600V AC permanent magnet motor, rated at 160hp/800Nm max and 94hp/400Nm continuous
Acts as a generator to recharge 600V / 4.8 kWh lithium-ion batteries during braking
Transmission Volvo AT2412E I-Shift gearbox
Twelve-speed automated transmission
Bodywork Wrightbus Bodywork (TBC)
Assembled in Northern Ireland and shipped to Singapore fully assembled
EDS To Be Confirmed

Being a diesel-electric hybrid bus, the Volvo 7900 Hybrid combines a conventional internal combustion engine propulsion system with an electric propulsion system. The small 4.7-litre diesel engine is supplemented by the Integrated Starter Alternator Motor (I-SAM) system, the key to its high fuel economy. The I-SAM system draws from the Lithium-Ion batteries and supplies additional power to the bus during periods of high energy demand directly to the drive train via a set of permanent-magnet motors, with a maximum output of 120kW and also powering other systems onboard the bus. The batteries are gradually recharged through regenerative braking. The I-SAM electric propulsion system hence reduces the load on the diesel engine, resulting in better fuel economy and lower vehicular emissions.

Another unique feature of the bus is the Volvo AT2412E I-Shift semi-automatic transmission, where the bus executes manual gear changes automatically, without any input from the driver. The bus accelerates in ‘steps’ very similar to a manual transmission, but the optimized transmission keeps the acceleration smooth.


See Also:
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