Patent GB-1193117-A (GB)
Title: Improvements in Power Assisted Braking Systems with Hydrostatic Safety Feature for Tractor Vehicle with or without Trailer
IPC: B60T7/04
Filed: 1967-10-05
Abstract: 1,193,117. Power assisted hydraulic brakes. REGIE NATIONALE DES USINES RENAULT. 5 Oct., 1967 [23 Nov., 1966], No. 45592/67. Headings F2E and F2F. In a tractor braking system the main source of fluid pressure to friction brake cylinders is a pump P (Fig. 1) driven by the tractor engine, and brake fluid pressure is provided by a pedal operated master cylinder if the pump fails or the engine is stopped. Unilateral braking selector valve.-Two pedals are provided on the tractor operable simultaneously or individually as for unilateral braking. Movement of a pedal, e.g. pedal 7 (Fig. 2) (section through II-II, Fig. 1), moves push rods 11, 13 to the left as shown, rotating against a torsion spring 20 a member 15 on a pin 17 (there being a similar member 16 operable by push rods 12, 14) so that a face 55 thereof is moved away from a rod 22 and a spring 56 closes a selector valve 4; while a rod 21 keeps selector valve 3 open. Thus the right hand brake is isolated and the left hand brake operated as described below. Power pump supplied braking.-On movement of the pedal (or pedals) an abutment 23 thereof engages a push member 25 (Fig. 1) which moves a slide valve 26 to the left. This valve 26 cuts off communication between a groove 48 and a cylinder 51 thus isolating the brakes from the reservoir R and opening up a passage between grooves 48 and 40 of both slide valve 26 and a coaxial slide valve 28 i.e. between the brake cylinders and the pump P. Moreover this movement of valve 26 throttles the passage between groove 40 and groove 41 i.e. between the feed line f 1  from the pump and a fluid outlet line f 2  to hydraulically operated appliances AG, thus causing an increase in pressure in groove 40 and in a pipe line leading to the brake cylinders via a port 49 linked to groove 40. The pressure in groove 40 also propagates via a duct 58 into an annular chamber 59 in which it actuates a differential piston 60 sliding on push member 25 and which contacts slide valve 28 pushing it to the left against a spring 61. The movement of valve 28 adjusts the amount of throttling between grooves 40 and 41 so that a fluid pressure necessary for the desired brake application is obtained. The longer the stroke of valve 26 to the left, the higher the pressure must be in chamber 59 (and therefore in the brake cylinders) for moving the slide valve 28 to its proper throttling position. Master cylinder-safety braking.-In the case of engine stoppage or pump failure, when the pedal (or pedals) is depressed the slide valve 26 acts as an intermediate push member engaging piston 31 of the master cylinder 2 moving the piston against a spring 64. This movement transmitted via a spring 32 and valve 35 will close a port 35 thus isolating the braking circuit of a trailer. Simultaneously pressure will rise in chamber 38 of the master cylinder being transmitted to the brake cylinders via a duct 37, open valves 3, 4 (Fig. 2) and ports 5, 6. Springs 63 are coupled to the brake pedals to enable a driver to "feel" the braking action.