Seats matter in a bus

Comatec involved in the design of a new seat for Khimaira

The leading manufacturer of bus seats in the Nordic countries, Khimaira Oy has extensive experience in the requirements of the industry and the changing needs of customers. Comatec is proficient in the mechanical design of commercial vehicles, which means that cooperation in designing seats with Khimaira is natural. The ongoing seat design project is also a good
example of how Comatec can benefit from cooperation between its own offices.

In its own seats, Khimaira focuses on light weight, dimensions, ergonomics and durability. Particular attention is paid to the passengers’ user experience and travel comfort.

Headquartered in Kalanti, Finland, Khimaira manufactures seats and upholstery for vehicles, trains, military vehicles and boats. Khimaira delivers seats in Finland and the rest of Europe. More than half of the company’s production is exported.

As the leading manufacturer of bus seats in the Nordic countries, Khimaira has extensive experience in the requirements of the industry and the changing needs of customers. Khimaira has built its business so that it can quickly and flexibly respond to its customers’ needs. This creates the basis for the entire business model. The customers’ strict quality requirements and criteria are followed in the case of small and large orders alike.

Special attention to user experience, travel comfort and safety

Passenger seats, interior upholstery, curtains and special seats for buses are part of Khimaira’s own bus industry product lines. Furthermore, many customers design their own seats but outsource their manufacture to Khimaira.

In its own seats, Khimaira focuses on light weight, dimensions, ergonomics and durability. Particular attention is paid to the passengers’ user experience and travel comfort.

“Comatec cooperates with Khimaira in the design of a new seat model, for example. The seat will be a finished product that suits large-scale production, which means that it will also be optimally priced. Did you know that the seats are the second most expensive part of a bus right after the chassis?” asks Engineering Manager Andrei Kotliar from Comatec.

“The seats are a key part of a bus, because the passengers will actually be touching the seat for the entire duration of their trip. In addition, seats are what they see in front of them. That is why you should invest in seat design.

“A prototype of the seat we designed for Khimaira was recently introduced at the Bus World trade fair, where it received praise on its ergonomics, in particular. The passenger experience is important for us and for Khimaira as well,” Andrei says.

“Safety should not be overlooked either. Safety requirements on seats are specified in the e-regulations published by the United Nations Economic Commission for Europe. The regulations list exact safety criteria and testing methods to verify compliance. A particularly challenging issue in the design of seats is the fact that the regulations include some mutually excluding properties: the seat must be sturdy but flexible too, for example.”

Testing is an important part of seat design

“An important part of seat design is the simulation and testing of the seats to verify compliance with the e-regulations. The tests are performed at our own location with equipment we have designed. Everything has been done in strict compliance with the requirements. We can also perform the statutory approval tests here, as long as we invite a representative of an accredited laboratory to supervise the test,” Andrei explains.

“A special characteristic of bus seats is the fact that unlike in a passenger vehicle, the seatbelt must be fully attached to the seat. The frame of the seat must be strong enough to withstand the high forces the seatbelts will experience in case of an accident. On the other hand, the seat must absorb the impact of the passenger behind the seat being thrown against the seat. This is to prevent passenger injuries. Reconciliation of these requirements is challenging and requires plenty of testing. Typically, several prototypes have to be made when developing a passenger seat.

“Simulation can reduce the need for testing. Creating a simulation model that is close enough to the actual conditions is extremely difficult due to the significant deformation of the seat. Comatec has focused on this problem with the help of a strain gauge analysis. The tested seat prototypes are equipped with strain gauges to obtain a clearer view of how the prototypes behave in the tests. The simulation model is fine-tuned based on the results to ensure that the results better correspond to reality. This way, each test serves the development of the seat frame and the simulation model. The simulation expertise obtained from the project can surely be utilised in future projects.”

Cooperation between offices to benefit customers

Members of the project design team (from the left): Engineering Manager Andrei Kotliar, Mechanical Design Engineer Minja Pönni, Structural Analyst Niko Finska and Mechanical Design Engineer Jarno Suurjärvi. The test bench that can be used for statutory testing is behind the team.

“The bench project has been a good indication of how easily Comatec can combine the special expertise of its different offices. Cooperation between offices is easy, because Comatec’s design process is the same at each office and for each design engineer,” Andrei explains.

“In this project, we utilised the strong expertise in commercial vehicle mechanics design at the Turku office and the strength calculation and simulation expertise of the Kuopio office. The best experts in strain gauge measuring were found at the Tampere office.

“Mechanical Design Engineers Minja Pönni and Jarno Suurjärvi from the Turku office participate in this project. Furthermore, Structural Analyst Niko Finska from the Kuopio office is involved in the strength design and simulation model development. Engineering Manager Suvi Petäjäjärvi and Testing Specialist Marko Ylinen from the Tampere office assist in the strain gauge measuring.

“We performed a strain gauge test on the frame of a seat at the Turku office, and Niko came to Turku in person for the test. We tested whether the prototype’s frame is strong enough and whether the back of the seat is flexible enough when subjected to a specific force. We also verified the actual stresses at specific points with strain gauges. We will use the test results to adjust the simulation model. We will also fine-tune the structure of the seat based on the test results.”

Cooperation with suppliers as well

“We like to cooperate with future suppliers as well, to introduce them to the project at an early stage so that we can take into account the requirements based on the manufacture of the different components, such as plastic components, in the design. This way, we can better optimise the manufacture, detect problems at an early stage and create the optimal final result for our customer,” Andrei explains..

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