Analysis of the Dynamics of a Hydraulic Control Circuit of an Automatic Gearbox

The description of the supply pressure hydraulic circuit and the couplings between its components are presented. A comparison between simulations and experiments is carried out. Using some linear facilities, it is possible to conclude that the low frequency modes mainly correspond to the wave effects of hydraulic lines which connect valves to each other.

In order to maintain a pressure in the supply circuit, an electronic pressure control is necessary. The design of a control law needs to build different linear models for different levels of pressure since the system is very non linear. Three transfer functions are found for three pressure levels. These transfer functions are very similar to the ones used by the automatic control department and obtained by experiments. Using these transfer functions it is possible to design the control law.

The “software tool” developed for this application uses state-of-the-art knowledge in hydraulics as well as in mechanical components used in gearboxes. This enables to connect, in a single tool, the electro-hydraulic control unit to each actuator and clutch the circuit has to control. This “tool” is introduced as a part of the V-cycle process of the automatic gearbox, from the design and development to the validation and test.