Volvo's BZR Electric chassis

Bus & Coach
Volvo’s new BZR Electric chassis combines existing technologies with a new cooling system while also offering customers a variety of locations to place the batteries. Ben Spencer reports from Sweden
(Image credit: Volvo Bus)

Electrification will clearly be an integral component in the journey towards decarbonisation, but there is no ‘one-size-fits-all’ solution when it comes to bus operations. Volvo understands the complexity of the task at hand and unveiled a customisable battery-electric chassis at a two-day preview event for World of Volvo – a 22,000m2 experience centre in Gothenburg, Sweden.

The BZR Electric is designed for city, intercity and commuter operations. The platform comes as a high-floor or low-entry layout, in two- or three-axle configurations, with a single or dual motor driveline. It accommodates lengths from 9.5 to 15m, a maximum weight of 27,000kg and traction power up to 400kW, or 540hp.

Fredrik Björn, product director city, business unit chassis, Volvo Buses, says the low-floor product is more sensitive to power inputs, so various aspects – such as the suspension and frame design – have been optimised. For markets that deal with worse street conditions or harsher environments, the high-floor platform is a sturdier solution. “A high-floor chassis is better for a high-floor or a low-entry bus, so it fills the gap for anyone not wanting a low-floor product. We offer a selection of rear axles, meaning we can operate with a higher average speed of 100kph, so we are closer to the commuter coach segment.”

The platform uses an existing driveline, battery monitoring and safety systems, but is most notable for the introduction of a new cooling system, which Björn describes as a passive/action system that can operate in two ways.

“If you have a cold enough ambient temperature, you don’t have to waste power on the compressor,” he explains. “If you have hot ambient temperatures and you need to cool the batteries lower than the ambient temperature, then you have an air condition cycle in the cooler where you can engage the compressor and make sure you get enough coolant to the batteries. The system offers different cooling modes that can be used when the vehicle is either charging or driving. It is intended to be an efficient, low-energy consuming cooling solution.”

Managing the temperature remains a challenge, partly because of the coolant needed for the driveline and batteries, but mainly due to the varying air conditioning needed for each bus. For example, buses operating in cities that have a 20°C year-round climate do not need air conditioning, whereas those operating in the Middle East or Australia could spend half the energy to keep the passengers cool. “In Nordic climates, if you are not allowed to operate the fuel combustion heater, then you are spending a lot of energy making sure the passengers are warm,” reasons Björn.


On the topic of energy, the BZR Electric comes with a variety of options for the position of the batteries, with operators having the choice of either four or six. Customers may want to place two batteries in front and behind the rear axles, while the high-floor configuration presents an option to place a battery behind the front axle. On low-entry vehicles, an operator may opt for placing two batteries on the front of the roof to optimise the weight distribution and avoid compromising the low-floor area.

To determine the most appropriate battery locations, Volvo collaborates with its market companies and the bodybuilder. “Each market has its own rules on axle pressures, passenger weight and the geometry of the vehicle, so it’s very hard to find a one-size-fits-all weight distribution. This is why we aim to offer as much flexibility as possible on the chassis,” says Björn.

Batteries aside, the BZR Electric also comes with a range of safety features, including an HVI Loop: a low voltage signal circuit that runs alongside the high voltage circuit to help improve safety in the workshop. “Wherever the high voltage [wire] goes, there is a separate wire that goes in and out of each component,” explains Björn. “The inclusion of this interlock loop would allow the system to recognise a connector that has been pulled out as an open circuit and would then close down the system and each component.”

The system also offers another safety feature for workers monitoring isolation resistance of a high voltage system and notice a tear in an orange cable.

“If there is less isolation resistance than our criteria, the system would then send fault codes and possibly even power down the system, depending on the severity of the issue,” he adds.


Away from bus components, there are plenty of other forward-looking technologies on the horizon from the Swedish bus company. On the second day of the preview event, Volvo demonstrated its latest innovations in the self-driving space by transporting attendees to the experience centre on a bus that uses autonomous docking technology.

To provide some context, the company has been assessing the use of this technology for some time now as part of a collaboration with Design and Human Factors at the Chalmers University of Technology. In 2021, the partners investigated how bus drivers experience autonomous driving support technology that activates when approaching a bus stop.

For the study, ten drivers from Keolis were filmed during 25 exercises as the autonomous drive technology assumed control of the bus when it approached the bus stop. The participants answered questionnaires and were interviewed before and after driving.

The results showed that the drivers felt the system was safe and convenient to use as they held onto the steering wheel less and less. Additionally, some drivers believe the system can contribute to better ergonomics by reducing tension in the neck and shoulders. “Bus drivers will dock a couple of hundred times every eight-hour shift and it can be a stressful environment,” explains chief project manager Joakim Jonsson. “The objective behind using autonomous docking technology is to help them perform optimally throughout the whole day.”

Furthermore, the system is expected to remove scenarios in which the bus could collide with roadside infrastructure, which would in turn lead to a reduction in maintenance.

For the demonstration, attendees boarded a 12m bus equipped with sensors, software and Volvo Dynamic Steering – a solution that takes control of the steering wheel once the driver has handed over control. “We communicate with the same CAN interface as used in the normal actuators only that we are enabling it to come from another ECU that is within the platform from Volvo Autonomous Solutions,” Jonsson explains. “The main computer is the brain that processes all the information, while the GNSS and GPS serve as the eyes and ears.”

Once onboard, the driver maintained a speed under 10kph before receiving a notification on a small display letting him know that he had met the criteria for the autonomous docking procedure. He then pressed a handover button on the dashboard as the technology controlled the speed and steering wheel angle.

In autonomous mode, the bus travelled in accordance with a pre-defined map. “The Lidar scan matches a digital map with the real-world surroundings. It was created by manual driving operations in which the sensors logged and stored all fixed features on the road infrastructure. When the data log is completed, it processes in a special map tool to a 3D map,” says Jonsson.

When arriving at the World of Volvo centre, the driver received a notification confirming the journey was complete.

Beyond this demonstration, a bus using this technology would then receive a follow-up notification highlighting the availability of an automated take-off option that can be initiated via the handover button. “This would be a controlled acceleration from a standstill to a suitable speed,” Jonsson continues. “The top speed would depend on the operation environment, but the bus driver would aim to take over at 15kph.”

But what would happen if a vulnerable road user entered the pathway of the docking procedure? “The driver will intervene by touching the brake sensor and resume manual driving,” confirms Jonsson.


Looking ahead, Volvo plans to integrate this technology on a 12-14km bus route in the area surrounding Västerås, a town located around 100km from Stockholm. The bus itself will have the capacity to transport up to 70 passengers in a trial that will span 30 bus stops.

“The route will go from the suburban area through the city core and outside the city. We will start outside the city centre and activate more stops over time to allow drivers to become more comfortable with the route,” he adds.

As part of the trial, Volvo will carry out another study with Chalmers University to understand driver preferences, which will then be used to further enhance the system. “I think we will use the same platform for docking in a depot and the first step will be to drive in environments with boundaries,” he adds. “One example could be between airport terminals and the final stage would be to drive fully autonomously in mixed traffic on certain routes.”

The BZR Electric and the autonomous docking technology are both pointing to a brighter future combining both innovation and sustainability.

With the World of Volvo centre now open to the public, there has never been a better time to swing by.


While the BZR is certainly one of the main attractions at the World of Volvo centre, there is a lot more going on outside of the main conference space. The top floor showcases a range of trucks, including the Volvo Titan and Volvo F88, while an exhibition on the ground floor highlights key milestones in the company’s journey.

Magnus Wrahme, CEO of World of Volvo, says: “With this experience centre, we can showcase our past, present and future. This is why the centre contains historic vehicles as well as docking stations, and an art installation that demonstrates sensor technology in a more contemporary packaging because we want to reach a broader audience. The centre gives something back to Gothenburg by offering a space for conferences and talks on technology and sustainability.”

Volvo is teaming up with Gothenburg Technical College to create experiments that will help inspire future engineers and technicians. These sessions will allow students to work together in teams to build structurally sound Lego models of vehicles. In the summer, students will be able to take part in an exercise that addresses the considerations for carrying out safety inspections on trucks.

Another co-lab exercise is a driver simulator. “The driver has to follow the road, but will receive different messages to change a song on the radio or apply the wipers,” says Wrahme. “This may cause them to come off the road, but the purpose of this task is to emphasise the importance of remaining focused while driving.”

Related content