Braking System Design for Vehicle and Trailer Combinations

This chapter extends the theory in Chapter 3 to the high-level design of braking systems for road vehicle and trailer combinations including car and light trailer (unbraked), motor vehicle and trailer with overrun (surge) brakes, motor vehicle with centre-axle trailer or chassis trailer, and articulated vehicle comprising tractor and semi-trailer. Force system equations are derived for each type of vehicle combination, and examples are provided to explain and discuss the features affecting braking system design for these types of vehicle, using adhesion utilisation and braking efficiency to demonstrate how the axle braking ratios and the distribution of braking between the towing vehicle and the trailer can be designed to avoid undesirable wheel-lock sequences. Load-sensing and compatibility considerations are explained, and because of the wide range of loading conditions under which vehicle combinations have to operate (including towing vehicle solo) it is explained why some form of variable braking distribution between the axles is essential.