Investigation of an Energy Efficient Hydraulic Propulsion System for a Railway Machine

Many railway construction and maintenance machines have large masses and perform repetitive working cycles with frequent stops that require precise positioning. For these reasons, a hydraulic propulsion system is a convenient choice. Common existing solutions make use of valve-controlled hydraulic circuits where inefficient fluid throttling takes place. Most of the time, dissipative braking is realized resulting in a remarkable quantity of available energy being wasted (up to 36 kJ of kinetic energy is available in the reference application). Additionally, the machine's automated positioning is a critical aspect. On some commercialized solutions, an overshoot of the desired final position is commonplace requiring a reverse motion in order to match the location of the desired working point. This is a negative characteristic as it introduces unnecessary fuel consumption and slows down productivity. Moreover, consideration of the limited adhesion in the wheel/rail interface is of critical importance. The propulsion system needs to be capable of differentiating the tractive or the braking torques between the driven axles. To this end, the paper proposes and analyzes a displacement-controlled (DC) propulsion system for a railway maintenance machine. The target is the removal of the fluid throttling mentioned above by defining an efficient hydraulic system. The ability to recover energy via regenerative breaking becomes a key process in improving the global machine efficiency. Simultaneously, an implementable control strategy is required for the proposed architecture to prevent overshoot of the desired position while stopping. To that end, this paper presents the mathematical model of the proposed layout used to simulate the system's behavior in order to confirm proper functioning. This work concludes with a discussion and definition of future improvements.