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Speed, load, and alternator control
Published in Raymond F. Gardner, Introduction to Plant Automation and Controls, 2020
The first governors were purely mechanical and proportional-only devices, where the flyweights were linked directly to the engine throttle to automatically modulate the input energy, see Figure 10.5 upper left for a small steam turbine governor. Next-generation governors became mechanical-hydraulic, where smaller flyweights could position a small pilot valve to hydraulically actuate a large steam valve. These mechanical-hydraulic governors used proportional control with feedback, employing spring closure of the governor valve (Figure 10.5 upper right). For more positive control and reduction of deadband, later-generation governors use small flyweights to actuate a small directional-control spool valve coupled hydraulically to a larger relay valve. The relay valve amplifies a small hydraulic signal into large actuating forces applied to the top or bottom of an operating-cylinder power piston. The positive hydraulic action to both open and close the governor valve essentially eliminates the hysteresis associated with a large spring (Figure 10.5 lower).
When is it too late to brake?
Published in Vehicle System Dynamics, 2022
Yang Chen, Zichen Zhang, Campbell Neighborgall, Mehdi Ahmadian
A schematic layout of a pneumatic brake system in a 33-ft A-double is shown in Figure 5. Upon braking, air is drawn from the air reservoir through the treadle valve and is delivered to the brake chambers of the steering axle, while passing on to the relay valves for the drive axle(s) and trailer(s) axles through the control line shown in red in Figure 5. The pressurised air in the control line signals the relay valve to charge the brake chambers from the brake reservoirs (marked in blue in Figure 5). The air pressure in the brake chamber pushes out the pushrod and presses the brake pads against the rotating drum to slow down the wheel rotation [40]. To reasonably simulate the complex braking dynamics, a pneumatic brake subsystem model is developed in Simulink® and integrated into TruckSim®. The details of the brake modelling that includes the brake delays and other effects present in LCVs are described in an earlier paper by the authors [41]. For brevity, the details of the brake model that is integrated into the co-simulation model are not included here. A high-level description of the model is included in Appendix B.