A high-efficiency regenerative shock absorber considering twin ball screws transmissions for application in range-extended electric vehicles
Nowadays we pay a lot for car fuel, the question is what happens to the fuel energy, how much of the fuel energy is used and how much is loosed, the answer is shocking, in a highway driving around 70% of the fuel energy is loosed due to engine imperfection, therefore the potential to use advanced technologies to increase fuel efficiency is enormous. One of these technologies is a regenerative shock absorber, the subject of this article. First, let me explain what a shock absorber is and how it works. In any driving, some amount of energy is converting to bothering energy, which is vibration, if the vibration reaches the passenger seat, makes them uncomfortable. Therefore, in a car, we have a device which is called a shock absorber. The shock absorber captures the vibration and provides us right comfort. The point is a conventional shock absorber cannot save energy, this device converts the captured vibrational energy to heat and waste energy. In other words, on utilizing a conventional shock absorber, the right comfort is achieved at the expense of fuel waste. However, by utilizing a regenerative shock absorber the scenario is different. The regenerative shock absorber captures the vibrational energy and provides us right comfort but instead of wasting energy this system converts the vibrational energy to electrical energy and stores it in a battery as a result by utilizing a regenerative shock absorber we can provide the right comfort, in addition, we can increase fuel efficiency. This system is a multi-application system, for example, this system can be scaled up to be used in a mining truck or can be scaled down and used in an ocean boat.
System design
The proposed system consists of four main modules: the suspension vibration input module, transmission mechanism module, generator module, and power storage module. When a vehicle is passing over an uneven road or changing speed, reciprocating linear vibrations from the two cylinders are inputted into the shock absorber, resulting in the nuts travelling downward or upward through the rods. The assembly of the cylinders, rods, and nuts is defined as the suspension vibration input module.
The transmission mechanism module transforms the reciprocating vibrations into unidirectional rotation of the generator shaft by utilizing a pair of ball screws with different rotation directions and screw pitches, a pair of overrun clutches, and a gear mechanism.
The generator module converts the mechanical energy of the unidirectional rotating shaft into electricity, which increases the efficiency of energy harvesting and reliability of the entire system. The energy is stored in the power storage module in supercapacitors, which are utilized to charge the batteries of EVs. Based on the irregularity of various excitation conditions and clearance of the overrun clutch when changing direction, the rotational speed of the generator is constantly changing. Therefore, the current outputted by the generator is unstable and irregular. A brushless DC motor generating a three-phase alternating current is used. Consequently, to enable the current to be steady and suitable for storage and charging, it is necessary to utilise a current rectifier and supercapacitors with voltage regulators as a power storage system. The rectifier circuit can rectify the three-phase alternating current into pulsed direct current.
