Development Of Accumulative Electro-hydraulic Power Steering System For Large And Medium-sized Commercial Vehicles

Commercial vehicle is the basic component of the highway transportation, which is a significant part of the national economy and people’s livelihood. Its importance is self-evident. At present, its quantity is huge in China and is growing fast accompanied with the economy development and road network construction. At the same time, the resource and environment problems we are facing are becoming more and more intense, so energy saving and environment protection technologies are more significant and should have attracted more focus.Since 1980 s, two kinds of innovative power steering technologies has come into use: the electro-hydraulic power steering(EHPS) and electric power steering(EPS), they both reduce the energy consumption sharply. Now in the field of passenger cars in China, more than a half of the power steering systems are EHPS or EPS, but due to many reasons, such as technology, cost, etc., these two kinds of power steering system has not yet spread among large and medium-sized commercial vehicles. Commercial vehicles are seen as a kind of production tools, whose designing concepts are different from passenger cars, but it meets the same demand and should have a consistent pursuit on energy conservation and emissions reduction with passenger cars. In addition, its quantity is huge, which is of the same order of magnitude with passenger cars. So, there is a real and urgent demand on a new type of power steering technology which is energy saving and suitable for large and medium-sized commercial vehicles.This paper researched on a new type of electro-hydraulic power steering system for large and medium-sized commercial vehicles. An accumulator was introduced in the proposed system as the direct power source of steering assistance, which sharply lowered down the power demand of the motor, meanwhile, provided enough assistant force. As a result, the proposed system was capable for the traditional power, hybrid power and alternative power large and medium-sized commercial vehicles. As the background of this research, the situation of the commercial vehicles and the power steering systems markets of China are described, recent years? quantities of production and ownership of large and medium-sized commercial vehicles are provided and some domestic and abroad researches about electro-hydraulic power steering system are discussed. After words, the working principle and characteristics of the proposed system and the researches about the key components of the proposed system, including the ECU, motor, accumulator and solenoid valve, are discussed.A prototype of the proposed EHPS system equipped with a 500 Watts brushless direct current motor and an accumulator with 6.3 liters nominal volume was capable for the vehicles with 4 tons steering axle load. The prototype was assembled on the ?Sailong 10? truck of the First Jiefang Automobile Manufacturing Corp and some road tests were conducted. The average power consumption was less than 300 Watts. The steering torque input on the steering wheel was about 5 N·m. A solenoid valve was introduced as the flow adjusting actuator, which made the assistant force adjustable according to the vehicle speed, so that an ideal assistant characteristics could be achieved by matching and control.