Design of a new transformation device for a tip seat for multifunctional public transportation

Design of a new transformation device for a tip seat for multifunctional public transportation

Van Vliet, E.

Happee, R. (mentor)
Van der Helm, F.C.T. (mentor)
Plettenburg, D.H. (mentor)

Mechanical, Maritime and Materials Engineering

BioMechanical Engineering

BME

2012-08-24

Tribus b.v. is a company in Utrecht that converts minibuses for multifunctional public transportation. This means that with the same bus both ambulant people and wheelchair occupants can be transported. The multifunctionality lies in the combination of a flexible floor layout and (tip) seats. The floor system is based on separate aluminium profiles that are assembled to form any desired floor layout. Tribus' tip seat FlexusPRO meets the highest quality and safety requirements. Because of its integrated three point safety belt, the seat can be positioned anywhere in the vehicle. A common seat layout is the 4x4 tip seats, where four FlexusPRO seats are positioned on the right side of the vehicle and four on the left. By folding the seat pan to the backrest and subsequently rotating the seat package to the side, a wheelchair environment is created without removing or repositioning the seat. This transformation from passenger seat (mode 1) to wheelchair space (mode 2) is an easy and fast operation that enables the transporter to do a combined transportation of ambulant people and wheelchair occupants with the same vehicle. Besides the benefits of Tribus' FlexusPRO, the tip seat also has some main drawbacks with respect to the production costs, weight, the available wheelchair space after seat transformation and the hindered view outside for the wheelchair occupant as a result of the seat dimensions in mode 2. The goal is to overcome these drawbacks, in order for Tribus to be able to launch a new tip seat that exceeds seats of competitors on price, weight, operation and functionality. The goal of this graduation project focuses on the improvements of the seat position in mode 2. This means an improvement of the transformation device, where the overall goal is to reduce the production costs and weight by at least 30% and increase the view outside for the wheelchair occupant by at least 20% in combination with an increased lateral wheelchair space of at least 10%. However, in order to obtain a good design, a complete concept of the new tip seat needs to be proposed, where every aspect of the seat is able to fulfil the design requirements. A morphological approach resulted in three tip seat concepts that are rated with respect to usage and manufacturing aspects. The final concept led to a tip seat with a rotation device and a tilting backrest, that increases the lateral wheelchair space in mode 2. The improvement of the lateral wheelchair space is however dependent on the entire seat design, where the base frame of the seat will be leading. Because the base frame of the seat is not part of this project, a specific percentage of the improvement is not yet known, but an improvement of at least 10% can be realized. The separate headrest of the seat is moved down during the transformation to mode 2, which improves the view outside for the wheelchair passenger. The entire seat design is also not part of this project, but research on commercial vehicles showed that a vertical adjustment of the headrest of 210 mm is possible, which would improve the view outside by approximately 33%. The new seat concept is used as a guideline for the design of the two mechanisms that are needed for the transformation from mode 1 to mode 2. The tilting motion of the backrest resulted in a mechanism that provides a simultaneous movement of both backrest and seat pan. The benefit is that the additional (tilting) functionality of the seat had no effect on the amount of operations needed for the transformation. The mechanism is based on the over-centre principle of a toggle clamp. The system uses four pivot points that connects the backrest to both seat pan and seat frame. This innovative solution resulted in the fact that no additional locking devices where necessary to prevent the angular movement of the backrest in mode 1. The loads on the three point belt in the backrest, as a result of a frontal impact, are transferred into the mechanism which is only locked by the geometry of the backrest and seat pan. This mechanism prevents additional costs and weight as a result of the additional tilting functionality. Finally a new rotation device is designed. The use of a morphological approach resulted in four concepts. The best concept is elaborated, resulting in a new steel swivel of 3 kg, which is a weight reduction of 38%. Because of the minimal amount of components, no welding operations and an easy and fast assembly, the cost price of the swivel is reduced by 47%. Both tilting mechanism and swivel have been prototyped and they underlined the benefits that are mentioned in this report. The swivel has even been tested by a physical pull test and passed this test successfully. The goal of reducing the production costs and weight by at least 30% has been exceeded on both aspects. The view outside for the wheelchair occupant could be improved by 33%, which also exceeds the required 20%. The required improvement of the lateral wheelchair space by 10% can still be realized and will exceed this 10% especially around the arms of the wheelchair occupant. The project has been a success and Tribus decided to continue the development of both mechanisms for series production.

http://resolver.tudelft.nl/uuid:1ed3d199-f73f-4569-9f5a-ae5236a38ee8

2017-08-24

Student theses

master thesis

(c) 2012 Van Vliet, E.