Julian Ewald

Selbstverstärkende hydraulische Bremse

Fahrerassistenzsysteme benotigen eine elektrische Schnittstelle zur Bremssteuerung auf niedrigem Leistungsniveau. Gleichzeitig soll aus Sicherheitsgrunden eine mechanische Ruckfallebene vorgesehen werden. Am Institut fur Fluidtechnische Antriebe und Steuerungen der RWTH Aachen wird eine selbstverstarkende hydraulische Bremse entwickelt, die diesen Zielkonflikt lost. Neben dem besonders geringen Energiebedarf zeichnet sie sich durch die Regelbarkeit des tatsachlichen Bremsmoments aus. Die dargestellten Messergebnisse demonstrieren das Entwicklungspotenzial der Bremse fur Kraft- und Nutzfahrzeuge.

Adjustable flow-control valve for the self-energising electro-hydraulic brake

Abstract This paper presents the design and performance of an electrically adjustable flow control valve. It is designed specifically for the self-energising electro-hydraulic brake which requires small volume flows, a fail-safe open characteristic, a leakage tight closed position, simple control by just one solenoid, good dynamics, and repeatability. The valve concept is based on a conventional pressure compensator design usually found in flow-control valves. The measuring orifice used to sense the flow through the valve is typically constant. In the presented design it is made adjustable using a hydro-mechanical pilot servo mechanism. The pilot is actuated by a proportional solenoid. The paper explains static flow equations used to parameterise the design. Dynamic simulation is used to validate the design before manufacturing. Measurements of the prototype show a good match with the simulation. Measurements of the main characteristics of the valve are shown, specifically the dynamic response to a step input as well as the flow-signal tracking and load pressure disturbance rejection behaviour. The valve is also tested in its target application, the self-energising electro-hydraulic brake, where it proves its effectiveness in normalising the response time of the non-linear and the inherently unstable brake. As opposed to a non-linear or gain-scheduling control, with the new valve the controller of the brake can be designed as a simple switching control. This is an advantage for the overall brakes safety evaluation and therefore helps to improve the prospects of using the self-energising brake in future applications such as rail vehicles.

Input–output linearisation applied to the brake torque control of the self-energising electro-hydraulic brake

This paper presents the controller for a self-energising electro-hydraulic brake. A non-linear controller is chosen for the brake torque control of the railway brake, which has the major benefit of achieving predictable dynamics of the brake torque build-up throughout the working range of the self-energising electro-hydraulic brake without controller adjustment. While being more complex in implementation, the non-linear controller is more straightforward in design compared to a proportional controller, which needs to be tuned empirically. This paper focuses on design of the controller, including the required simplification of the mathematical model to the third order. Simulation results show that the desired dynamics can be achieved. Test rig measurements confirm the applicability of the non-linear brake torque controller.

The self-energising hydraulic brake

Driver assistance systems require for low-power electrical interfaces for braking control. At the same time for safety reasons a mechanical fallback level should be provided. At the Institute of Fluid Power Drives and Controls of the RWTH Aachen University (Germany) an innovative Self-Energising Hydraulic Brake is being developed to solve this conflict of objectives. Besides its low power consumption it features a closed loop control of the actual braking torque. The presented measuring results demonstrate the brake’s development potential for cars and utility vehicles.