Hydraulic anti-skid braking systems for vehicles

Claim 1

An anti-skid braking system for a four wheel vehicle having brakes on the front and rear wheels, wherein said system comprises first and seond brake-applying circuits, said first circuit comprising a first source of brake-applying fluid, and a first connection between the first source and the brake on one of said front wheels and the brake on the diagonally opposite one of said rear wheels, and the second circuit comprising a second source of brake-applying fluid, and a second connection between the brake on the other of said front wheels and the brake on the diagonally opposite other of said rear wheels, a first modulator located in said first connection for modulating the supply of fluid from said first source to both said brakes on the said one front wheel and said diagonally opposite rear wheel, a second modulator located in said second connection for modulating the supply of fluid from said second source to both said brakes on the said other front wheel and the said diagonally opposite other rear wheel, four skid sensors, each for providing a skid signal dependent upon the behaviour of a respective one of said wheels, a control module for operating at least one of said modulators in accordance with the nature of at least one skid signal, and apportioning valves disposed between said modulators and said brakes on said rear wheels, said control module being constructed and arranged to ignore a skid signal from said sensor on one of said rear wheels until a skid signal is also received from said sensor on the other of said rear wheels, whereafter said control module is operative to operate one of said two modulators.