Styrtransmission för bandfordon

Sammanfattning: The purpose of this master thesis is to construct a steering transmission, for a tracked vehicle, containing two hydraulic circuits which are connected. The steering transmission should be mechanical to avoid steer-by-wire. BAE Systems Hägglunds has in an earlier study examined a system with two hydraulic pumps and one hydraulic motor, but the safety of the system wasn’t sufficient. To achieve sufficient redundancy there must be two hydraulic motors, which are controlled separately. When the two systems are connected in one point, this point is a critical part of the system because it directly affects both circuits. If one of the hydraulic circuits fails the other should be able to operate independently as a steering transmission. This is possible by disconnecting the defect circuit with a tooth clutch. Separating the systems can also be done with a differential. Using a differential means that the use of a brake or a bidirectional no-back control is necessary to prevent the drive shaft from going backwards. The tracked vehicle should be able to make a pivot turn in less then 12 s, with a vehicle weight of 17500 kg. That combined with lack of space set high demands on the hydraulic system. The hydraulic components which are used must withstand pressure up to 450 bar and flows up to 170 l/min. The hydraulic pumps must cope with the drive circuit’s speed of 4400 rpm. The hydraulic pumps must have a variable displacement so that the vehicle will be able to turn in both directions. The hydraulic motor have a fixed displacement, this makes construction of the mechanical linkage from the steering wheel to the hydraulic system easier. Push/pull wires will be used as linkage. The system can easily be redimensioned to fit a heavier vehicle. It’s easy to shift the concept to a differential style if any problems appear during testing. The system is a part of a component test that will be carried out during 2006.