GB1349145A - Vehicle braking - Google Patents

Abstract

1349145 Rail-sanding devices GIRLING Ltd 25 June 1971 [14 April 1970] 17671/70 Heading B7J [Also in Divisions G1 and H4] Means controlling the movement of a wheel 2 or 3 of a vehicle 1 comprises a tachometer generator (16) Figs. 2, 3 (not shown), driven from the vehicle transmission through drive means causing the generator to rotate at a speed higher than that of the wheel thereby producing an electrical signal representative of rotation of the wheel, circuit means including a capacitor 46 arranged to derive from said signal a further signal representative of the change of speed of the wheel and means including transistors 47, 51, 55 and 57 and solenoid 61 responsive to the further signal attaining a predetermined value to actuate by way of air valve 9 a sander 6 which applies sand to the rail 4 over which the wheel rolls to increase the coefficient of friction therebetween. To compensate for low speed response, gain-control means is actuated when tachogenerator speed falls below 150 RPM. Thus transistor 71 is fed with a speed dependent voltage from potentiometer 88 so that as speed falls transistor 71 is progressively turned off to introduce resistor 69 in series with resistor 70 in the negative feedback path controlling the gain of an amplifier comprising transistors 51, 55, 57 and 60. The sanding means is arranged to be additionally alternatively operable manually. A stationary sanding means arranged to act, e.g. upon a steep incline may be responsive to a signal provided from a vehicle negotiating the incline.