DEVELOPMENT OF A MODEL OF ENERGY SAVING ELECTRO HYDRAULIC POWER-STEERING SYSTEM

Abstract

Automobile steering system is used to steer a vehicle to the desired path. In mechanical steering system, the driver’s physical effort is used to steer front wheels. But during parking or at slow speeds, steering becomes difficult and energy-consuming because of high friction. Conventional power steering uses hydraulic power to reduce steering effort. The objective of this work is to develop an energy-saving model of electro hydraulic power steering system of vehicle that can save energy and also provide a good steering feel to driver according to vehicle speed and steering rate. Similar systems can be found in Ford, Volkswagen, Audi, and Nissan cars. At first, the model was simulated in Matlab software and then hardware was developed. A set of experiments has been carried out to setup the electro-hydraulic power steering (EHPS) system test bench. The pressure developed in hydraulic chamber is proportional to motor speed. So, the motor speed is controlled via PID controller to regulate the hydraulic pressure according to vehicle speed and steering rate. Fuzzy-logic is applied to tune the proportional (𝐾𝑝) and integral (𝐾𝑖) gain of the PID controller. Experimental results show that the response of the system is fast because of the use of fuzzy logic, which improves the steering feel. An Arduino microcontroller is used to implement the fuzzy-PID algorithm to control the DC motor. The experimental results show that the energy consumption of the proposed model is low compared to conventional hydraulic power steering. Power consumption is calculated for five different torques: 0 Nm, 3.98 Nm, 4.23 Nm, 4.48 Nm, and 5.23 Nm. At high vehicle speeds, the proposed model can save more energy. If set point is greater than current motor speed (set point is 45 and current RPS is 22), then PID saves 0.038505Wh more electrical energy than fuzzy-PID at 0 Nm torque for 10 sec, but it can’t develop the right hydraulic pressure at the right time. If the set point is less than the current motor speed, then fuzzy-PID saves 0.02599 Wh of electrical energy compared to PID at 0 Nm torque for 10 sec, and it can provide sufficient hydraulic power at the right time. For energy saving electrohydraulic power steering system, the correlation of electric power with voltage, current, motor speed, and vehicle speed at 0 Nm torque is 𝑃8 = −181.823 −33.4625v+23.8562i+0*n+0.46321V and the correlation of hydraulic power with hydraulic pressure, pump discharge rate, motor speed, and vehicle speed at 3.98 Nm torque is 𝑃ℎ8 =−4.2179+ 2.3687p+0*q+0*n+0.0241V.