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In this article forklift walking part optimized in structure is first introduced. The traditional mechanical or hydrodynamic transmission is simplified and designed for hydraulic drive form. According to the requirements of forklift starting, braking, reversing and changing speed, the design of the variable pump quantitative motor closed circuit is adopted. That mean, that motor output torque is determined by the load not the speed change. Speed ranges widly, and the forklift can be running smoothly under the maximum speed range in the maximum load. The speed is adjusted by the pump displacement. Because the hydraulic system has the characteristics of high power-transmitted density, stable starting reverse, easily frequent operation and automatic control, etc., it simplifies the structure of forklift running part. It not only meets the requirements of vehicle smoothly starting and braking, but also can complete stepless speed change conveniently and gear reducing for good operation. Therefore, it simplifies the structure of energy transfer to adopt the pump motor speed closed type volume oil circuit.There are hydraulic drives in every part after the structure is optimized. It brings great convenience for the production and detection of forklift. There are many obvious nonlinear characteristics between fault phenomena and reason in the hydraulic system. So it is reasonable to describe the fault phenomena and reasons with fuzzy concepts. In all kinds of hydraulic systems, there are some common characteristics, as a result of certain similarities between systems and components. In this area, there are much expert experiences; it creates good condition for the development of fault diagnosis expert system. Full hydraulic forklift system consists of 5 parts, as below:walking hydraulic system, steering hydraulic system, lifting hydraulic system, inclined hydraulic system, belongings hydraulic system. Each hydraulic system is composed of some components and circuit. In this article it can sort and classify fault symptoms which are showed in the hydraulic system, using fuzzy methods, for example in steering system. Refer to the probability values caused by fault reasons to establish membership, then adopt fuzzy reasoning analyze the parameter error, at last find out the cause of the malfunction; or using the measuring instrument and the sensor to gain fault parameter changes, and make the error of parameters fuzzy, then adopt control analyze the parameter error to find out the cause of the malfunction.
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