A Purely Mechanical Energy Storing Concept for Hybrid Vehicles
The paper contains the design and simulation of a purely mechanical system for storing energy during vehicle deceleration, which can be utilized during subsequent acceleration (regenerative braking). A continuously variable transmission (CVT) regulates the energy transfer, energy storage is accomplished by means of a spiral spring and additional use of a planetary transmission. The transmission ratio of the CVT is adapted by a combined feed-forward and feed-back control. A computer simulation for a vehicle with an overall mass of 1500kg, and an energy storage capacity of 30kJ was performed for different driving cycles. In a typical urban stop and go situation the proposed device will save up to 0.72kg fuel per 100km and the overall efficiency analysis together with simple design, easy recycling, and long life expectance, showed a clear advantage over other hybrid concepts for frequent stops and accelerations.
An electro-mechanical braking energy recovery system based on coil springs for energy saving applications in electric vehicles
Abstract Regenerative braking system is a promising energy recovery mechanism to achieve energy saving in EVs (electric vehicles). This paper focuses on a novel mechanical and electrical dual-pathway braking energy recovery system (BERS) based on coil springs for energy saving applications in EVs. With the aims of maximizing energy recovery efficiency, mechanical and electrical recovery strategies are respectively employed under two different brake situations of inching braking and emergency braking. This system mainly consists of three parts, including the mechanical module, electrical module and control module. The mechanical module utilizes coil springs to store the kinetic energy in the form of elastic potential energy which can be utilized to provide a part of the starting torque for EVs. The electrical module enables recovery of the braking energy into the vehicle battery. The control module controls the mechanical module and the electrical module to work coordinately to select an appropriate energy recovery pathway under different braking modes. A full-size prototype, manufactured and based on this design, is introduced. Simulations and experiments of the proposed regenerative braking system are conducted to verify the system. Auxiliary starting torque of 12.7 N m, maximum voltage of 3.5 V and total energy recovery efficiencies of 0.53 can be obtained, verifying that the proposed braking energy recovery system is effective and beneficial for vehicle energy savings.
Numerical analysis of surface crack propagation in flexible pavements using XFEM and cohesive zone model
Surface initiated (top-down) cracking in the longitudinal direction of pavements has become a predominant mode of failure in thick asphalt pavements. Most previous researchers studied crack propagation using the traditional Linear Elastic Fracture Mechanics (LEFM) method by calculating the stress intensity factor around the crack tip. In this paper, Extended Finite Element Method (XFEM) was used to study the key factors causing surface initiated crack propagation under surface tension and/or shear. A two-dimensional (2-D) finite element (FE) model for a two-lane flexible pavement was built to predict pavement responses and crack propagation potential under various scenarios. It was found that surface tension is the major driving force for crack propagation when the crack is at some distance away from tire loading. The results show that the distance from the location of crack to tire loading, the depth and direction of the crack, and the modulus ratio between the hot-mix asphalt (HMA) layer and the base layer have significant influences on crack propagation under surface tension. On the other hand, this study shows that shear stress can induce surface initiated crack propagation near the loading area as the shear resistance of material becomes low at the high temperature.