Abstract: It is pointed out that the transient response of a valve-controlled asymmetric hydraulic cylinder is the result of the alternate action of its oil circuits in positive and negative directions in accordance with the principal on the structural characteristic of the system. In view of the defects of the old modeling manner in which the models is incorporated via the definition of load pressure and load rate of flow without thinking of the effects of the system structure on the models, a segmental transfer function is presented as a unified frequency domain model for valve-controlled cylinder. This function consists of two sub-functions corresponding respectively to the two oil circuits mentioned above. For a symmetric hydraulic cylinder, the two sub-functions equate each other both in structure and in parameters; For an asymmetric hydraulic cylinder, the sub-functions aren’t identical in their speed amplification ratio Kv1 and Kv2, the functions can be incorporated via the incorporation of Kv1 and Kv2. Based on analysis of the structural parameters and of the configuration of response curve of transfer functions, the relationship between the incorporation arithmetic of the models and the damp, attenuation ratio of system is studied by means of digital simulation with a series of typical systems. A concept and method of variable-incorporation and parameter-incorporation is presented, and then a plan is put forward with which an equivalent transfer function can be obtained via incorporation of the segmental transfer function. The step response of the equivalent function quite coincides against that of digital simulation for normal hydraulic servo systems. The subjected models are evidently more accurate than the previous one.

Key words: Analysis of frequency domain, Asymmetric-cylinder, Hydraulic pressure, Modeling