In this paper, electric and hydraulic regeneration methods of recovering potential energy from an electro-hydraulic forklift truck are studied. Two similar forklift setups equipped with either electric or direct hydraulic energy storage are compared. In the first setup, the forklift lifting system is controlled directly with an electric servomotor drive. The servomotor drives a hydraulic pump capable of also operating as a hydraulic motor during lowering motion. In the second setup, the hydraulically operated forklift is equipped with an energy recovery system consisting of pressure accumulators for storing energy and a hydraulic digital valve package for precise leakage free flow control. This paper describes the arrangements of the experimental setups. The results of the proposed systems are then compared from the energy efficiency point of view. Energy-savings ratios for electric and hydraulic test systems were calculated for different fork velocities and payloads.

Traditionally, a typical hydraulic circuit utilized in stationary industrial applications is based on valve operated actuation. One realization of such a system is a constant pressure circuit employing a hydraulic accumulator as an energy reserve and pressure stabilizer. The pump is used to maintain the desired pressure level, for example by using a variable displacement pump that controls the displacement setting based on the pressure level. The main benefit of this system architecture is its ability to produce high output powers with a very low response time. However, it is not the most energy efficient and in many cases, not the most space efficient solution. The efficiency of this system type is reduced mainly by the need to choke the pressure difference between the set system pressure and the actual pressure need in the actuator. By directly controlling the actuator via controlling the pump’s output flow with an electric servo motor, the throttling losses of the valve controlled system can be avoided. In addition, this enables the usage of closed circuits which in terms removes the need for a large reservoir. In this study, the replacement of a valve controlled hydraulic system with a pump controlled system in an industrial stationary material handling machine is investigated. The machine’s work cycle consist of continuous consecutive lifting and lowering motions of one end of a platform pivoted at the opposite end. The study consist of designing the replacing circuit topology, of dimensioning the hydraulic components utilizing a created Simulink-based tool and of a simulation based analysis on the dynamic properties of the designed hydraulic system.

No abstract

We predict heavy quark production cross sections in Deep Inelastic Scattering at high energy by applying the Color Glass Condensate effective theory. We demonstrate that when the calculation is performed consistently at next-to-leading order accuracy with massive quarks it becomes possible, for the first time in the dipole picture with perturbatively calculated center-of-mass energy evolution, to simultaneously describe both light and heavy quark production data at small xBj. We furthermore show how the heavy quark cross section data provides additional strong constraints on the extracted non-perturbative initial condition for the small-xBj evolution equations.

No abstract