The thesis developed and tested a novel slip-control pneumatic emergency braking system for heavy goods vehicles, incorporating a novel binary-actuated pneumatic valve and a sliding-mode slip controller. The prototype system was installed and tested on one of the CVDC's experimental heavy vehicles, and demonstrated 16% reduction in stopping distance compared to a conventional anti-lock braking system. The work was performed in collaboration with Haldex Brake Products, Camcon and other members of the Cambridge Vehicle Dynamics Consortium www.cvdc.org.
The over-representation of Heavy Goods Vehicles (HGVs) in accident data can be attributed to several undesirable attributes of their dynamics. These include: rearward amplification, lateral off-tracking and relatively long emergency stopping distances. Previous studies by the Cambridge Vehicle Dynamics Consortium (CVDC) have suggested that, by improving the control bandwidth of conventional HGV brake actuators and using a ‘slip control’ braking strategy, HGV stopping distances could be reduced by up to 30% over existing systems. The work covered in this thesis looks to validate these predictions through Hardware-in-the-Loop (HiL) simulation and vehicle tests.
An introduction to HGV brake hardware and control is presented in Chapter 1. This is followed by straight-line braking simulations of an HGV using a HiL test rig in Chapter 2. In these tests, a conventional Anti-Lock Braking System (ABS) is compared to a prototype braking system consisting of high-speed pneumatic valves (designed by a previous CVDC researcher) and a sliding mode slip controller. Results indicate that the novel system could reduce stopping distances and air consumption by 21% and 17% respectively.
Chapter 3 considers the influence of longitudinal tyre dynamics on the straight-line braking performance of a HGV slip control system. Two vibration modes involving the tyre tread band and wheel hub (an in-phase mode at 20Hz, and an anti-phase mode at 55Hz) influence the performance of the slip control system. It is shown that a gain scheduled sliding mode slip controller can be designed to be robust to oscillations in wheel speed associated with these modes.
Chapter 4 focuses on the design of a next generation high-speed ABS modulator valve suitable for installation on a test vehicle. Prototype valves blocks are built and shown to meet the requirements of a typical UK semitrailer. Frequency response tests with the new valves indicate that the system can achieve a pressure control bandwidth of 10Hz, significantly higher than the previous generation high-speed valve system (6Hz) and conventional ABS hardware (1.5Hz).
Chapter 5 discusses installation of High-speed ABS modulator valves on a tri-axle semitrailer. Straight-line braking tests are then carried out in Chapter 6 – comparing the new valve system with conventional ABS. On average, a 16% reduction in stopping distance is achieved by the slip control high-speed valve system. Air consumption and Mean Absolute Slip Error (MSE) are also reduced by 52% and 68% respectively.
Conclusions and recommendations for future work are discussed in Chapter 7.