The Control System

Abstract

A block diagram of a hydrostatic transmission described in Chapter 5 was shown in Fig. 5.5. A block diagram of a valve operated control system is shown in Fig. 7.1. The major feature distinguishing the two systems is the part played by the pump. In the hydrostatic transmission the pump performs the dual role of power source and control element, whereas in the valve-operated system it acts as the power source to the control element. Both systems configurations can be represented by a single block diagram, Fig. 7.2. Since in the majority of cases the controller will produce an electrical low-power signal, an additional element is required to process this signal in order to provide a signal compatible with the control element input characteristics. This element is designated as the electro-hydraulic interface in the block diagrams, Fig. 7.2.