| Summary: | Freno AB in Piteå has developed a tractor with a semi-trailer based on a Volkswagen Crafter chassis. The modifications of the vehicle that are included in this thesis work covers the parking brake system of the semitrailer, the rear underrun protection device of the tractor and the maneuvering of the trailer’s service brake. The manufacturer of the tractor requests an independent analysis of whether these modifications have negative influences on the vehicle.A description of the parking brake system was made and its function was analyzed using force and torque equilibrium. The parking brake of the semi-trailer is maneuvered by an electric signal from the switch controlling the parking brake indicator on the dash board. The results were compared with regulations applicable by the date of the vehicle’s service entry. In theory, the parking brake meets the legal requirement to keep the vehicle stationary in a hill with 16 % slope and the design requirement of 18 %.Regulations regarding the rear underrun protection were studied and the company’s contact person was interviewed about the modification’s procedure. The underrun protection device has been moved forwards due to the shortening of the rear overhang. No modification has been made to the device itself that can affect its strength. According to EU Directive 70/221/EC, rear underrun protection is not necessary for this vehicle type.For the maneuvering system of the semi-trailer’s service brakes, the designer was interviewed and a system description was formulated. The trailer’s service brakes are maneuvered by a directional valve connected to the tractor’s brake circuits. This valve is the only interface between the tractor and the semitrailer brake circuits. The maximum consumption of brake fluid caused by the directional valve is 0.3 cm3. A test method was produced to determine if pressure variations caused by the semi-trailer’s ABS system can be measured in the tractors brake circuits. The measurements are to be implemented with a pressure sensor connected ...
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